From 571354a942739aca9a4c11f9b99287572f974ff1 Mon Sep 17 00:00:00 2001
From: Valentyn Kolesnikov <javadev75@gmail.com>
Date: Sun, 10 Dec 2023 19:19:52 +0200
Subject: [PATCH] Added tasks 73-98

---
 README.md                                     | 28 +++++++
 src/main/php/com_github_leetcode/TreeNode.php | 52 +++++++++++++
 .../s0073_set_matrix_zeroes/Solution.php      | 63 ++++++++++++++++
 .../s0073_set_matrix_zeroes/readme.md         | 36 +++++++++
 .../s0074_search_a_2d_matrix/Solution.php     | 35 +++++++++
 .../s0074_search_a_2d_matrix/readme.md        | 31 ++++++++
 .../g0001_0100/s0075_sort_colors/Solution.php | 31 ++++++++
 .../g0001_0100/s0075_sort_colors/readme.md    | 41 +++++++++++
 .../Solution.php                              | 41 +++++++++++
 .../s0076_minimum_window_substring/readme.md  | 42 +++++++++++
 .../php/g0001_0100/s0078_subsets/Solution.php | 28 +++++++
 .../php/g0001_0100/s0078_subsets/readme.md    | 25 +++++++
 .../g0001_0100/s0079_word_search/Solution.php | 70 ++++++++++++++++++
 .../g0001_0100/s0079_word_search/readme.md    | 41 +++++++++++
 .../Solution.php                              | 73 +++++++++++++++++++
 .../readme.md                                 | 28 +++++++
 .../Solution.php                              | 48 ++++++++++++
 .../readme.md                                 | 48 ++++++++++++
 .../Solution.php                              | 23 ++++++
 .../readme.md                                 | 23 ++++++
 .../Solution.php                              | 41 +++++++++++
 .../readme.md                                 | 34 +++++++++
 .../s0073_set_matrix_zeroes/SolutionTest.php  | 21 ++++++
 .../s0074_search_a_2d_matrix/SolutionTest.php | 19 +++++
 .../s0075_sort_colors/SolutionTest.php        | 21 ++++++
 .../SolutionTest.php                          | 22 ++++++
 .../g0001_0100/s0078_subsets/SolutionTest.php | 19 +++++
 .../s0079_word_search/SolutionTest.php        | 25 +++++++
 .../SolutionTest.php                          | 17 +++++
 .../SolutionTest.php                          | 27 +++++++
 .../SolutionTest.php                          | 17 +++++
 .../SolutionTest.php                          | 26 +++++++
 32 files changed, 1096 insertions(+)
 create mode 100644 src/main/php/com_github_leetcode/TreeNode.php
 create mode 100644 src/main/php/g0001_0100/s0073_set_matrix_zeroes/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0073_set_matrix_zeroes/readme.md
 create mode 100644 src/main/php/g0001_0100/s0074_search_a_2d_matrix/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0074_search_a_2d_matrix/readme.md
 create mode 100644 src/main/php/g0001_0100/s0075_sort_colors/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0075_sort_colors/readme.md
 create mode 100644 src/main/php/g0001_0100/s0076_minimum_window_substring/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0076_minimum_window_substring/readme.md
 create mode 100644 src/main/php/g0001_0100/s0078_subsets/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0078_subsets/readme.md
 create mode 100644 src/main/php/g0001_0100/s0079_word_search/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0079_word_search/readme.md
 create mode 100644 src/main/php/g0001_0100/s0084_largest_rectangle_in_histogram/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0084_largest_rectangle_in_histogram/readme.md
 create mode 100644 src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/readme.md
 create mode 100644 src/main/php/g0001_0100/s0096_unique_binary_search_trees/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0096_unique_binary_search_trees/readme.md
 create mode 100644 src/main/php/g0001_0100/s0098_validate_binary_search_tree/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0098_validate_binary_search_tree/readme.md
 create mode 100644 src/test/php/g0001_0100/s0073_set_matrix_zeroes/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0074_search_a_2d_matrix/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0075_sort_colors/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0076_minimum_window_substring/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0078_subsets/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0079_word_search/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0084_largest_rectangle_in_histogram/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0094_binary_tree_inorder_traversal/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0096_unique_binary_search_trees/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0098_validate_binary_search_tree/SolutionTest.php

diff --git a/README.md b/README.md
index beedb7d..703881d 100644
--- a/README.md
+++ b/README.md
@@ -69,6 +69,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0074 |[Search a 2D Matrix](src/main/php/g0001_0100/s0074_search_a_2d_matrix/Solution.php)| Medium | Top_100_Liked_Questions, Array, Binary_Search, Matrix, Big_O_Time_O(endRow+endCol)_Space_O(1) | 9 | 68.18
 
 #### Day 9
 
@@ -254,6 +255,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0096 |[Unique Binary Search Trees](src/main/php/g0001_0100/s0096_unique_binary_search_trees/Solution.php)| Medium | Top_100_Liked_Questions, Dynamic_Programming, Math, Tree, Binary_Tree, Binary_Search_Tree, Big_O_Time_O(n)_Space_O(1) | 0 | 100.00
 
 #### Day 12
 
@@ -642,6 +644,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0098 |[Validate Binary Search Tree](src/main/php/g0001_0100/s0098_validate_binary_search_tree/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree, Big_O_Time_O(N)_Space_O(log(N)) | 10 | 70.97
 
 #### Day 9 Graph/BFS/DFS
 
@@ -723,6 +726,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0074 |[Search a 2D Matrix](src/main/php/g0001_0100/s0074_search_a_2d_matrix/Solution.php)| Medium | Top_100_Liked_Questions, Array, Binary_Search, Matrix, Big_O_Time_O(endRow+endCol)_Space_O(1) | 9 | 68.18
 | 0033 |[Search in Rotated Sorted Array](src/main/php/g0001_0100/s0033_search_in_rotated_sorted_array/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Binary_Search, Big_O_Time_O(log_n)_Space_O(1) | 7 | 83.17
 
 #### Day 9 Binary Search Tree
@@ -755,6 +759,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
 | 0003 |[Longest Substring Without Repeating Characters](src/main/php/g0001_0100/s0003_longest_substring_without_repeating_characters/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Hash_Table, Sliding_Window, Big_O_Time_O(n)_Space_O(1) | 4 | 99.33
+| 0076 |[Minimum Window Substring](src/main/php/g0001_0100/s0076_minimum_window_substring/Solution.php)| Hard | Top_100_Liked_Questions, Top_Interview_Questions, String, Hash_Table, Sliding_Window, Big_O_Time_O(s.length())_Space_O(1) | 21 | 100.00
 
 #### Day 15 Tree
 
@@ -819,6 +824,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 |-|-|-|-|-|-
 | 0001 |[Two Sum](src/main/php/g0001_0100/s0001_two_sum/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Big_O_Time_O(n)_Space_O(n) | 9 | 97.47
 | 0055 |[Jump Game](src/main/php/g0001_0100/s0055_jump_game/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Greedy, Big_O_Time_O(n)_Space_O(1) | 129 | 74.56
+| 0075 |[Sort Colors](src/main/php/g0001_0100/s0075_sort_colors/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Sorting, Two_Pointers, Big_O_Time_O(n)_Space_O(1) | 3 | 88.78
 | 0041 |[First Missing Positive](src/main/php/g0001_0100/s0041_first_missing_positive/Solution.php)| Hard | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Big_O_Time_O(n)_Space_O(n) | 111 | 90.48
 
 #### Udemy Two Pointers
@@ -843,7 +849,9 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0074 |[Search a 2D Matrix](src/main/php/g0001_0100/s0074_search_a_2d_matrix/Solution.php)| Medium | Top_100_Liked_Questions, Array, Binary_Search, Matrix, Big_O_Time_O(endRow+endCol)_Space_O(1) | 9 | 68.18
 | 0048 |[Rotate Image](src/main/php/g0001_0100/s0048_rotate_image/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Math, Matrix, Big_O_Time_O(n^2)_Space_O(1) | 4 | 81.58
+| 0073 |[Set Matrix Zeroes](src/main/php/g0001_0100/s0073_set_matrix_zeroes/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Matrix, Big_O_Time_O(m\*n)_Space_O(1) | 37 | 61.76
 | 0056 |[Merge Intervals](src/main/php/g0001_0100/s0056_merge_intervals/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Sorting, Big_O_Time_O(n_log_n)_Space_O(n) | 48 | 80.00
 
 #### Udemy Linked List
@@ -858,6 +866,8 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0094 |[Binary Tree Inorder Traversal](src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Stack, Big_O_Time_O(n)_Space_O(n) | 3 | 82.09
+| 0098 |[Validate Binary Search Tree](src/main/php/g0001_0100/s0098_validate_binary_search_tree/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree, Big_O_Time_O(N)_Space_O(log(N)) | 10 | 70.97
 
 #### Udemy Trie and Heap
 
@@ -884,6 +894,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 |-|-|-|-|-|-
 | 0022 |[Generate Parentheses](src/main/php/g0001_0100/s0022_generate_parentheses/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Dynamic_Programming, Backtracking, Big_O_Time_O(2^n)_Space_O(n) | 4 | 83.67
 | 0039 |[Combination Sum](src/main/php/g0001_0100/s0039_combination_sum/Solution.php)| Medium | Top_100_Liked_Questions, Array, Backtracking, Big_O_Time_O(2^n)_Space_O(n+2^n) | 11 | 87.10
+| 0078 |[Subsets](src/main/php/g0001_0100/s0078_subsets/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Bit_Manipulation, Backtracking, Big_O_Time_O(2^n)_Space_O(n\*2^n) | 7 | 69.23
 | 0017 |[Letter Combinations of a Phone Number](src/main/php/g0001_0100/s0017_letter_combinations_of_a_phone_number/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Hash_Table, Backtracking, Big_O_Time_O(4^n)_Space_O(n) | 5 | 60.19
 | 0046 |[Permutations](src/main/php/g0001_0100/s0046_permutations/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Backtracking, Big_O_Time_O(n\*n!)_Space_O(n+n!) | 4 | 92.42
 
@@ -925,6 +936,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0074 |[Search a 2D Matrix](src/main/php/g0001_0100/s0074_search_a_2d_matrix/Solution.php)| Medium | Top_100_Liked_Questions, Array, Binary_Search, Matrix, Big_O_Time_O(endRow+endCol)_Space_O(1) | 9 | 68.18
 
 #### Day 6 String
 
@@ -952,6 +964,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0094 |[Binary Tree Inorder Traversal](src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Stack, Big_O_Time_O(n)_Space_O(n) | 3 | 82.09
 
 #### Day 11 Tree
 
@@ -972,6 +985,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0098 |[Validate Binary Search Tree](src/main/php/g0001_0100/s0098_validate_binary_search_tree/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree, Big_O_Time_O(N)_Space_O(log(N)) | 10 | 70.97
 
 ### Data Structure II
 
@@ -985,6 +999,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0075 |[Sort Colors](src/main/php/g0001_0100/s0075_sort_colors/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Sorting, Two_Pointers, Big_O_Time_O(n)_Space_O(1) | 3 | 88.78
 | 0056 |[Merge Intervals](src/main/php/g0001_0100/s0056_merge_intervals/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Sorting, Big_O_Time_O(n_log_n)_Space_O(n) | 48 | 80.00
 
 #### Day 3 Array
@@ -1174,6 +1189,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 |-|-|-|-|-|-
 | 0034 |[Find First and Last Position of Element in Sorted Array](src/main/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Binary_Search, Big_O_Time_O(log_n)_Space_O(1) | 19 | 81.01
 | 0033 |[Search in Rotated Sorted Array](src/main/php/g0001_0100/s0033_search_in_rotated_sorted_array/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Binary_Search, Big_O_Time_O(log_n)_Space_O(1) | 7 | 83.17
+| 0074 |[Search a 2D Matrix](src/main/php/g0001_0100/s0074_search_a_2d_matrix/Solution.php)| Medium | Top_100_Liked_Questions, Array, Binary_Search, Matrix, Big_O_Time_O(endRow+endCol)_Space_O(1) | 9 | 68.18
 
 #### Day 2 Binary Search
 
@@ -1216,6 +1232,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0078 |[Subsets](src/main/php/g0001_0100/s0078_subsets/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Bit_Manipulation, Backtracking, Big_O_Time_O(2^n)_Space_O(n\*2^n) | 7 | 69.23
 
 #### Day 10 Recursion Backtracking
 
@@ -1229,6 +1246,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 |-|-|-|-|-|-
 | 0017 |[Letter Combinations of a Phone Number](src/main/php/g0001_0100/s0017_letter_combinations_of_a_phone_number/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Hash_Table, Backtracking, Big_O_Time_O(4^n)_Space_O(n) | 5 | 60.19
 | 0022 |[Generate Parentheses](src/main/php/g0001_0100/s0022_generate_parentheses/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Dynamic_Programming, Backtracking, Big_O_Time_O(2^n)_Space_O(n) | 4 | 83.67
+| 0079 |[Word Search](src/main/php/g0001_0100/s0079_word_search/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Matrix, Backtracking, Big_O_Time_O(4^(m\*n))_Space_O(m\*n) | 697 | 100.00
 
 #### Day 12 Dynamic Programming
 
@@ -1289,6 +1307,16 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | #    |      Title     | Difficulty  | Tag         | Time, ms | Time, %
 |------|----------------|-------------|-------------|----------|---------
+| 0098 |[Validate Binary Search Tree](src/main/php/g0001_0100/s0098_validate_binary_search_tree/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree, Data_Structure_I_Day_14_Tree, Level_1_Day_8_Binary_Search_Tree, Udemy_Tree_Stack_Queue, Big_O_Time_O(N)_Space_O(log(N)) | 10 | 70.97
+| 0096 |[Unique Binary Search Trees](src/main/php/g0001_0100/s0096_unique_binary_search_trees/Solution.php)| Medium | Top_100_Liked_Questions, Dynamic_Programming, Math, Tree, Binary_Tree, Binary_Search_Tree, Dynamic_Programming_I_Day_11, Big_O_Time_O(n)_Space_O(1) | 0 | 100.00
+| 0094 |[Binary Tree Inorder Traversal](src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Stack, Data_Structure_I_Day_10_Tree, Udemy_Tree_Stack_Queue, Big_O_Time_O(n)_Space_O(n) | 3 | 82.09
+| 0084 |[Largest Rectangle in Histogram](src/main/php/g0001_0100/s0084_largest_rectangle_in_histogram/Solution.php)| Hard | Top_100_Liked_Questions, Top_Interview_Questions, Array, Stack, Monotonic_Stack, Big_O_Time_O(n_log_n)_Space_O(log_n) | 298 | 100.00
+| 0079 |[Word Search](src/main/php/g0001_0100/s0079_word_search/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Matrix, Backtracking, Algorithm_II_Day_11_Recursion_Backtracking, Big_O_Time_O(4^(m\*n))_Space_O(m\*n) | 697 | 100.00
+| 0078 |[Subsets](src/main/php/g0001_0100/s0078_subsets/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Bit_Manipulation, Backtracking, Algorithm_II_Day_9_Recursion_Backtracking, Udemy_Backtracking/Recursion, Big_O_Time_O(2^n)_Space_O(n\*2^n) | 7 | 69.23
+| 0076 |[Minimum Window Substring](src/main/php/g0001_0100/s0076_minimum_window_substring/Solution.php)| Hard | Top_100_Liked_Questions, Top_Interview_Questions, String, Hash_Table, Sliding_Window, Level_2_Day_14_Sliding_Window/Two_Pointer, Big_O_Time_O(s.length())_Space_O(1) | 21 | 100.00
+| 0075 |[Sort Colors](src/main/php/g0001_0100/s0075_sort_colors/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Sorting, Two_Pointers, Data_Structure_II_Day_2_Array, Udemy_Arrays, Big_O_Time_O(n)_Space_O(1) | 3 | 88.78
+| 0074 |[Search a 2D Matrix](src/main/php/g0001_0100/s0074_search_a_2d_matrix/Solution.php)| Medium | Top_100_Liked_Questions, Array, Binary_Search, Matrix, Data_Structure_I_Day_5_Array, Algorithm_II_Day_1_Binary_Search, Binary_Search_I_Day_8, Level_2_Day_8_Binary_Search, Udemy_2D_Arrays/Matrix, Big_O_Time_O(endRow+endCol)_Space_O(1) | 9 | 68.18
+| 0073 |[Set Matrix Zeroes](src/main/php/g0001_0100/s0073_set_matrix_zeroes/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Matrix, Udemy_2D_Arrays/Matrix, Big_O_Time_O(m\*n)_Space_O(1) | 37 | 61.76
 | 0072 |[Edit Distance](src/main/php/g0001_0100/s0072_edit_distance/Solution.php)| Hard | Top_100_Liked_Questions, String, Dynamic_Programming, Algorithm_II_Day_18_Dynamic_Programming, Dynamic_Programming_I_Day_19, Udemy_Dynamic_Programming, Big_O_Time_O(n^2)_Space_O(n2) | 29 | 75.00
 | 0070 |[Climbing Stairs](src/main/php/g0001_0100/s0070_climbing_stairs/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Dynamic_Programming, Math, Memoization, Algorithm_I_Day_12_Dynamic_Programming, Dynamic_Programming_I_Day_2, Level_1_Day_10_Dynamic_Programming, Udemy_Dynamic_Programming, Big_O_Time_O(n)_Space_O(n) | 3 | 82.81
 | 0064 |[Minimum Path Sum](src/main/php/g0001_0100/s0064_minimum_path_sum/Solution.php)| Medium | Top_100_Liked_Questions, Array, Dynamic_Programming, Matrix, Dynamic_Programming_I_Day_16, Udemy_Dynamic_Programming, Big_O_Time_O(m\*n)_Space_O(m\*n) | 20 | 81.48
diff --git a/src/main/php/com_github_leetcode/TreeNode.php b/src/main/php/com_github_leetcode/TreeNode.php
new file mode 100644
index 0000000..5ee3d70
--- /dev/null
+++ b/src/main/php/com_github_leetcode/TreeNode.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace leetcode\com_github_leetcode;
+
+class TreeNode {
+    public $val;
+    public $left;
+    public $right;
+
+    function __construct($val, $left = null, $right = null) {
+        $this->val = $val;
+        $this->left = $left;
+        $this->right = $right;
+    }
+
+    public static function create($treeValues) {
+        $root = empty($treeValues) ? null : new TreeNode($treeValues[0]);
+        $queue = array();
+        array_push($queue, $root);
+        $i = 1;
+        while ($i < count($treeValues)) {
+            $curr = array_shift($queue);
+            if ($treeValues[$i] != null) {
+                $curr->left = new TreeNode($treeValues[$i]);
+                array_push($queue, $curr->left);
+            }
+            if (++$i < count($treeValues) && $treeValues[$i] != null) {
+                $curr->right = new TreeNode($treeValues[$i]);
+                array_push($queue, $curr->right);
+            }
+            $i++;
+        }
+        return $root;
+    }
+
+    public function __toString() {
+        if ($this->left == null && $this->right == null) {
+            return "" . $this->val;
+        } else {
+            $root = "" . $this->val;
+            $leftValue = "null";
+            $rightValue = "null";
+            if ($this->left != null) {
+                $leftValue = $this->left->__toString();
+            }
+            if ($this->right != null) {
+                $rightValue = $this->right->__toString();
+            }
+            return $root . "," . $leftValue . "," . $rightValue;
+        }
+    }
+}
diff --git a/src/main/php/g0001_0100/s0073_set_matrix_zeroes/Solution.php b/src/main/php/g0001_0100/s0073_set_matrix_zeroes/Solution.php
new file mode 100644
index 0000000..d79b08d
--- /dev/null
+++ b/src/main/php/g0001_0100/s0073_set_matrix_zeroes/Solution.php
@@ -0,0 +1,63 @@
+<?php
+
+namespace leetcode\g0001_0100\s0073_set_matrix_zeroes;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Hash_Table #Matrix
+// #Udemy_2D_Arrays/Matrix #Big_O_Time_O(m*n)_Space_O(1)
+// #2023_12_10_Time_37_ms_(61.76%)_Space_23.4_MB_(44.12%)
+
+class Solution {
+    /**
+     * @param Integer[][] $matrix
+     * @return NULL
+     */
+    public function setZeroes(&$matrix) {
+        $m = count($matrix);
+        $n = count($matrix[0]);
+        $row0 = false;
+        $col0 = false;
+        // Check if 0th col needs to be market all 0s in future
+        foreach ($matrix as $ints) {
+            if ($ints[0] == 0) {
+                $col0 = true;
+                break;
+            }
+        }
+        // Check if 0th row needs to be market all 0s in future
+        for ($i = 0; $i < $n; $i++) {
+            if ($matrix[0][$i] == 0) {
+                $row0 = true;
+                break;
+            }
+        }
+        // Store the signals in 0th row and column
+        for ($i = 1; $i < $m; $i++) {
+            for ($j = 1; $j < $n; $j++) {
+                if ($matrix[$i][$j] == 0) {
+                    $matrix[$i][0] = 0;
+                    $matrix[0][$j] = 0;
+                }
+            }
+        }
+        // Mark 0 for all cells based on signal from 0th row and 0th column
+        for ($i = 1; $i < $m; $i++) {
+            for ($j = 1; $j < $n; $j++) {
+                if ($matrix[$i][0] == 0 || $matrix[0][$j] == 0) {
+                    $matrix[$i][$j] = 0;
+                }
+            }
+        }
+        // Set 0th column
+        for ($i = 0; $i < $m; $i++) {
+            if ($col0) {
+                $matrix[$i][0] = 0;
+            }
+        }
+        // Set 0th row
+        for ($i = 0; $i < $n; $i++) {
+            if ($row0) {
+                $matrix[0][$i] = 0;
+            }
+        }
+    }
+}
diff --git a/src/main/php/g0001_0100/s0073_set_matrix_zeroes/readme.md b/src/main/php/g0001_0100/s0073_set_matrix_zeroes/readme.md
new file mode 100644
index 0000000..404b556
--- /dev/null
+++ b/src/main/php/g0001_0100/s0073_set_matrix_zeroes/readme.md
@@ -0,0 +1,36 @@
+73\. Set Matrix Zeroes
+
+Medium
+
+Given an `m x n` integer matrix `matrix`, if an element is `0`, set its entire row and column to `0`'s, and return _the matrix_.
+
+You must do it [in place](https://en.wikipedia.org/wiki/In-place_algorithm).
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/08/17/mat1.jpg)
+
+**Input:** matrix = [[1,1,1],[1,0,1],[1,1,1]]
+
+**Output:** [[1,0,1],[0,0,0],[1,0,1]] 
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2020/08/17/mat2.jpg)
+
+**Input:** matrix = [[0,1,2,0],[3,4,5,2],[1,3,1,5]]
+
+**Output:** [[0,0,0,0],[0,4,5,0],[0,3,1,0]] 
+
+**Constraints:**
+
+*   `m == matrix.length`
+*   `n == matrix[0].length`
+*   `1 <= m, n <= 200`
+*   <code>-2<sup>31</sup> <= matrix[i][j] <= 2<sup>31</sup> - 1</code>
+
+**Follow up:**
+
+*   A straightforward solution using `O(mn)` space is probably a bad idea.
+*   A simple improvement uses `O(m + n)` space, but still not the best solution.
+*   Could you devise a constant space solution?
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0074_search_a_2d_matrix/Solution.php b/src/main/php/g0001_0100/s0074_search_a_2d_matrix/Solution.php
new file mode 100644
index 0000000..cbaf249
--- /dev/null
+++ b/src/main/php/g0001_0100/s0074_search_a_2d_matrix/Solution.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace leetcode\g0001_0100\s0074_search_a_2d_matrix;
+
+// #Medium #Top_100_Liked_Questions #Array #Binary_Search #Matrix #Data_Structure_I_Day_5_Array
+// #Algorithm_II_Day_1_Binary_Search #Binary_Search_I_Day_8 #Level_2_Day_8_Binary_Search
+// #Udemy_2D_Arrays/Matrix #Big_O_Time_O(endRow+endCol)_Space_O(1)
+// #2023_12_10_Time_9_ms_(68.18%)_Space_19.8_MB_(51.82%)
+
+class Solution {
+    /**
+     * @param Integer[][] $matrix
+     * @param Integer $target
+     * @return Boolean
+     */
+    public function searchMatrix($matrix, $target) {
+        $endRow = count($matrix);
+        $endCol = count($matrix[0]);
+        $targetRow = 0;
+        $result = false;
+        for ($i = 0; $i < $endRow; $i++) {
+            if ($matrix[$i][$endCol - 1] >= $target) {
+                $targetRow = $i;
+                break;
+            }
+        }
+        for ($i = 0; $i < $endCol; $i++) {
+            if ($matrix[$targetRow][$i] == $target) {
+                $result = true;
+                break;
+            }
+        }
+        return $result;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0074_search_a_2d_matrix/readme.md b/src/main/php/g0001_0100/s0074_search_a_2d_matrix/readme.md
new file mode 100644
index 0000000..ce4e033
--- /dev/null
+++ b/src/main/php/g0001_0100/s0074_search_a_2d_matrix/readme.md
@@ -0,0 +1,31 @@
+74\. Search a 2D Matrix
+
+Medium
+
+Write an efficient algorithm that searches for a value in an `m x n` matrix. This matrix has the following properties:
+
+*   Integers in each row are sorted from left to right.
+*   The first integer of each row is greater than the last integer of the previous row.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/10/05/mat.jpg)
+
+**Input:** matrix = [[1,3,5,7],[10,11,16,20],[23,30,34,60]], target = 3
+
+**Output:** true 
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2020/10/05/mat2.jpg)
+
+**Input:** matrix = [[1,3,5,7],[10,11,16,20],[23,30,34,60]], target = 13
+
+**Output:** false 
+
+**Constraints:**
+
+*   `m == matrix.length`
+*   `n == matrix[i].length`
+*   `1 <= m, n <= 100`
+*   <code>-10<sup>4</sup> <= matrix[i][j], target <= 10<sup>4</sup></code>
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0075_sort_colors/Solution.php b/src/main/php/g0001_0100/s0075_sort_colors/Solution.php
new file mode 100644
index 0000000..8f49374
--- /dev/null
+++ b/src/main/php/g0001_0100/s0075_sort_colors/Solution.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace leetcode\g0001_0100\s0075_sort_colors;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Sorting #Two_Pointers
+// #Data_Structure_II_Day_2_Array #Udemy_Arrays #Big_O_Time_O(n)_Space_O(1)
+// #2023_12_10_Time_3_ms_(88.78%)_Space_19.2_MB_(20.41%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return NULL
+     */
+    public function sortColors(&$nums) {
+        $zeroes = 0;
+        $ones = 0;
+        for ($i = 0; $i < count($nums); $i++) {
+            if ($nums[$i] == 0) {
+                $nums[$zeroes++] = 0;
+            } elseif ($nums[$i] == 1) {
+                $ones++;
+            }
+        }
+        for ($j = $zeroes; $j < $zeroes + $ones; $j++) {
+            $nums[$j] = 1;
+        }
+        for ($k = $zeroes + $ones; $k < count($nums); $k++) {
+            $nums[$k] = 2;
+        }
+    }
+}
diff --git a/src/main/php/g0001_0100/s0075_sort_colors/readme.md b/src/main/php/g0001_0100/s0075_sort_colors/readme.md
new file mode 100644
index 0000000..4062c6f
--- /dev/null
+++ b/src/main/php/g0001_0100/s0075_sort_colors/readme.md
@@ -0,0 +1,41 @@
+75\. Sort Colors
+
+Medium
+
+Given an array `nums` with `n` objects colored red, white, or blue, sort them **[in-place](https://en.wikipedia.org/wiki/In-place_algorithm)** so that objects of the same color are adjacent, with the colors in the order red, white, and blue.
+
+We will use the integers `0`, `1`, and `2` to represent the color red, white, and blue, respectively.
+
+You must solve this problem without using the library's sort function.
+
+**Example 1:**
+
+**Input:** nums = [2,0,2,1,1,0]
+
+**Output:** [0,0,1,1,2,2] 
+
+**Example 2:**
+
+**Input:** nums = [2,0,1]
+
+**Output:** [0,1,2] 
+
+**Example 3:**
+
+**Input:** nums = [0]
+
+**Output:** [0] 
+
+**Example 4:**
+
+**Input:** nums = [1]
+
+**Output:** [1] 
+
+**Constraints:**
+
+*   `n == nums.length`
+*   `1 <= n <= 300`
+*   `nums[i]` is `0`, `1`, or `2`.
+
+**Follow up:** Could you come up with a one-pass algorithm using only constant extra space?
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0076_minimum_window_substring/Solution.php b/src/main/php/g0001_0100/s0076_minimum_window_substring/Solution.php
new file mode 100644
index 0000000..fd31c15
--- /dev/null
+++ b/src/main/php/g0001_0100/s0076_minimum_window_substring/Solution.php
@@ -0,0 +1,41 @@
+<?php
+
+namespace leetcode\g0001_0100\s0076_minimum_window_substring;
+
+// #Hard #Top_100_Liked_Questions #Top_Interview_Questions #String #Hash_Table #Sliding_Window
+// #Level_2_Day_14_Sliding_Window/Two_Pointer #Big_O_Time_O(s.length())_Space_O(1)
+// #2023_12_10_Time_21_ms_(100.00%)_Space_19.5_MB_(89.09%)
+
+class Solution {
+    /**
+     * @param String $s
+     * @param String $t
+     * @return String
+     */
+    public function minWindow($s, $t) {
+        $map = array_fill(0, 128, 0);
+        for ($i = 0; $i < strlen($t); $i++) {
+            $map[ord($t[$i]) - ord('A')]++;
+        }
+        $count = strlen($t);
+        $begin = 0;
+        $end = 0;
+        $d = PHP_INT_MAX;
+        $head = 0;
+        while ($end < strlen($s)) {
+            if ($map[ord($s[$end++]) - ord('A')]-- > 0) {
+                $count--;
+            }
+            while ($count == 0) {
+                if ($end - $begin < $d) {
+                    $d = $end - $begin;
+                    $head = $begin;
+                }
+                if ($map[ord($s[$begin++]) - ord('A')]++ == 0) {
+                    $count++;
+                }
+            }
+        }
+        return $d == PHP_INT_MAX ? "" : substr($s, $head, $head + $d);
+    }
+}
diff --git a/src/main/php/g0001_0100/s0076_minimum_window_substring/readme.md b/src/main/php/g0001_0100/s0076_minimum_window_substring/readme.md
new file mode 100644
index 0000000..7c7d492
--- /dev/null
+++ b/src/main/php/g0001_0100/s0076_minimum_window_substring/readme.md
@@ -0,0 +1,42 @@
+76\. Minimum Window Substring
+
+Hard
+
+Given two strings `s` and `t` of lengths `m` and `n` respectively, return _the **minimum window substring** of_ `s` _such that every character in_ `t` _(**including duplicates**) is included in the window. If there is no such substring__, return the empty string_ `""`_._
+
+The testcases will be generated such that the answer is **unique**.
+
+A **substring** is a contiguous sequence of characters within the string.
+
+**Example 1:**
+
+**Input:** s = "ADOBECODEBANC", t = "ABC"
+
+**Output:** "BANC"
+
+**Explanation:** The minimum window substring "BANC" includes 'A', 'B', and 'C' from string t. 
+
+**Example 2:**
+
+**Input:** s = "a", t = "a"
+
+**Output:** "a"
+
+**Explanation:** The entire string s is the minimum window. 
+
+**Example 3:**
+
+**Input:** s = "a", t = "aa"
+
+**Output:** ""
+
+**Explanation:** Both 'a's from t must be included in the window. Since the largest window of s only has one 'a', return empty string. 
+
+**Constraints:**
+
+*   `m == s.length`
+*   `n == t.length`
+*   <code>1 <= m, n <= 10<sup>5</sup></code>
+*   `s` and `t` consist of uppercase and lowercase English letters.
+
+**Follow up:** Could you find an algorithm that runs in `O(m + n)` time?
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0078_subsets/Solution.php b/src/main/php/g0001_0100/s0078_subsets/Solution.php
new file mode 100644
index 0000000..3b97ae6
--- /dev/null
+++ b/src/main/php/g0001_0100/s0078_subsets/Solution.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace leetcode\g0001_0100\s0078_subsets;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Bit_Manipulation #Backtracking
+// #Algorithm_II_Day_9_Recursion_Backtracking #Udemy_Backtracking/Recursion
+// #Big_O_Time_O(2^n)_Space_O(n*2^n) #2023_12_10_Time_7_ms_(69.23%)_Space_19.5_MB_(84.62%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer[][]
+     */
+    public function subsets($nums) {
+        $res = array();
+        $this->solve($nums, array(), $res, 0);
+        return $res;
+    }
+
+    private function solve($nums, $temp, &$res, $start) {
+        array_push($res, $temp);
+        for ($i = $start; $i < count($nums); $i++) {
+            array_push($temp, $nums[$i]);
+            $this->solve($nums, $temp, $res, $i + 1);
+            array_pop($temp);
+        }
+    }
+}
diff --git a/src/main/php/g0001_0100/s0078_subsets/readme.md b/src/main/php/g0001_0100/s0078_subsets/readme.md
new file mode 100644
index 0000000..2bd42ee
--- /dev/null
+++ b/src/main/php/g0001_0100/s0078_subsets/readme.md
@@ -0,0 +1,25 @@
+78\. Subsets
+
+Medium
+
+Given an integer array `nums` of **unique** elements, return _all possible subsets (the power set)_.
+
+The solution set **must not** contain duplicate subsets. Return the solution in **any order**.
+
+**Example 1:**
+
+**Input:** nums = [1,2,3]
+
+**Output:** [[],[1],[2],[1,2],[3],[1,3],[2,3],[1,2,3]] 
+
+**Example 2:**
+
+**Input:** nums = [0]
+
+**Output:** [[],[0]] 
+
+**Constraints:**
+
+*   `1 <= nums.length <= 10`
+*   `-10 <= nums[i] <= 10`
+*   All the numbers of `nums` are **unique**.
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0079_word_search/Solution.php b/src/main/php/g0001_0100/s0079_word_search/Solution.php
new file mode 100644
index 0000000..e01f3cb
--- /dev/null
+++ b/src/main/php/g0001_0100/s0079_word_search/Solution.php
@@ -0,0 +1,70 @@
+<?php
+
+namespace leetcode\g0001_0100\s0079_word_search;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Matrix #Backtracking
+// #Algorithm_II_Day_11_Recursion_Backtracking #Big_O_Time_O(4^(m*n))_Space_O(m*n)
+// #2023_12_10_Time_599_ms_(100.00%)_Space_19_MB_(79.49%)
+
+class Solution {
+    /**
+     * @param String[][] $board
+     * @param String $word
+     * @return Boolean
+     */
+    public function exist($board, $word) {
+        $wordCountMap = [];
+        for ($i = 0; $i < strlen($word); $i++) {
+            $char = $word[$i];
+            if (isset($wordCountMap[$char])) {
+                $wordCountMap[$char] += 1;
+            } else {
+                $wordCountMap[$char] = 1;
+            }
+        }
+        $positions = [];
+        foreach ($board as $rowIdx => $items) {
+            foreach ($items as $colIdx => $item) {
+                if ($item === $word[0]) {
+                    $positions[] = [$rowIdx, $colIdx];
+                }
+                if (isset($wordCountMap[$item])) {
+                    $wordCountMap[$item]--;
+                }
+            }
+        }
+        foreach ($wordCountMap as $count) {
+            if ($count > 0) {
+                return false;
+            }
+        }
+        foreach ($positions as $position) {
+            if ($this->dfs($board, $word, 0, $position)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    function dfs($board, $word, $index, $position) {
+        [$x, $y] = $position;
+        if (!isset($board[$x][$y])) {
+            return false;
+        }
+        if ($board[$x][$y] !== $word[$index]) {
+            return false;
+        } elseif ($index === strlen($word) - 1) {
+            return true;
+        }
+        $board[$x][$y] = '-1';
+        $dirs = [[0, 1], [0, -1], [1, 0], [-1, 0]];
+        foreach ($dirs as $dir) {
+            $newX = $x + $dir[0];
+            $newY = $y + $dir[1];
+            if ($this->dfs($board, $word, $index + 1, [$newX, $newY])) {
+                return true;
+            }
+        }
+        return false;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0079_word_search/readme.md b/src/main/php/g0001_0100/s0079_word_search/readme.md
new file mode 100644
index 0000000..0500297
--- /dev/null
+++ b/src/main/php/g0001_0100/s0079_word_search/readme.md
@@ -0,0 +1,41 @@
+79\. Word Search
+
+Medium
+
+Given an `m x n` grid of characters `board` and a string `word`, return `true` _if_ `word` _exists in the grid_.
+
+The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/11/04/word2.jpg)
+
+**Input:** board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCCED"
+
+**Output:** true 
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2020/11/04/word-1.jpg)
+
+**Input:** board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "SEE"
+
+**Output:** true 
+
+**Example 3:**
+
+![](https://assets.leetcode.com/uploads/2020/10/15/word3.jpg)
+
+**Input:** board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCB"
+
+**Output:** false 
+
+**Constraints:**
+
+*   `m == board.length`
+*   `n = board[i].length`
+*   `1 <= m, n <= 6`
+*   `1 <= word.length <= 15`
+*   `board` and `word` consists of only lowercase and uppercase English letters.
+
+**Follow up:** Could you use search pruning to make your solution faster with a larger `board`?
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0084_largest_rectangle_in_histogram/Solution.php b/src/main/php/g0001_0100/s0084_largest_rectangle_in_histogram/Solution.php
new file mode 100644
index 0000000..1eaeba5
--- /dev/null
+++ b/src/main/php/g0001_0100/s0084_largest_rectangle_in_histogram/Solution.php
@@ -0,0 +1,73 @@
+<?php
+
+namespace leetcode\g0001_0100\s0084_largest_rectangle_in_histogram;
+
+// #Hard #Top_100_Liked_Questions #Top_Interview_Questions #Array #Stack #Monotonic_Stack
+// #Big_O_Time_O(n_log_n)_Space_O(log_n) #2023_12_10_Time_298_ms_(100.00%)_Space_31.6_MB_(80.00%)
+
+class Solution {
+    /**
+     * @param Integer[] $heights
+     * @return Integer
+     */
+    public function largestRectangleArea($heights) {
+        return $this->largestArea($heights, 0, count($heights));
+    }
+
+    private function largestArea($a, $start, $limit) {
+        if ($a == null || empty($a)) {
+            return 0;
+        }
+        if ($start == $limit) {
+            return 0;
+        }
+        if ($limit - $start == 1) {
+            return $a[$start];
+        }
+        if ($limit - $start == 2) {
+            $maxOfTwoBars = max($a[$start], $a[$start + 1]);
+            $areaFromTwo = min($a[$start], $a[$start + 1]) * 2;
+            return max($maxOfTwoBars, $areaFromTwo);
+        }
+        if ($this->checkIfSorted($a, $start, $limit)) {
+            $maxWhenSorted = 0;
+            for ($i = $start; $i < $limit; $i++) {
+                if ($a[$i] * ($limit - $i) > $maxWhenSorted) {
+                    $maxWhenSorted = $a[$i] * ($limit - $i);
+                }
+            }
+            return $maxWhenSorted;
+        } else {
+            $minInd = $this->findMinInArray($a, $start, $limit);
+            return $this->maxOfThreeNums(
+                $this->largestArea($a, $start, $minInd),
+                $a[$minInd] * ($limit - $start),
+                $this->largestArea($a, $minInd + 1, $limit));
+        }
+    }
+
+    private function findMinInArray($a, $start, $limit) {
+        $min = PHP_INT_MAX;
+        $minIndex = -1;
+        for ($index = $start; $index < $limit; $index++) {
+            if ($a[$index] < $min) {
+                $min = $a[$index];
+                $minIndex = $index;
+            }
+        }
+        return $minIndex;
+    }
+
+    private function checkIfSorted($a, $start, $limit) {
+        for ($i = $start + 1; $i < $limit; $i++) {
+            if ($a[$i] < $a[$i - 1]) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private function maxOfThreeNums($a, $b, $c) {
+        return max(max($a, $b), $c);
+    }
+}
diff --git a/src/main/php/g0001_0100/s0084_largest_rectangle_in_histogram/readme.md b/src/main/php/g0001_0100/s0084_largest_rectangle_in_histogram/readme.md
new file mode 100644
index 0000000..96ca2d0
--- /dev/null
+++ b/src/main/php/g0001_0100/s0084_largest_rectangle_in_histogram/readme.md
@@ -0,0 +1,28 @@
+84\. Largest Rectangle in Histogram
+
+Hard
+
+Given an array of integers `heights` representing the histogram's bar height where the width of each bar is `1`, return _the area of the largest rectangle in the histogram_.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2021/01/04/histogram.jpg)
+
+**Input:** heights = [2,1,5,6,2,3]
+
+**Output:** 10
+
+**Explanation:** The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area, which has an area = 10 units. 
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2021/01/04/histogram-1.jpg)
+
+**Input:** heights = [2,4]
+
+**Output:** 4 
+
+**Constraints:**
+
+*   <code>1 <= heights.length <= 10<sup>5</sup></code>
+*   <code>0 <= heights[i] <= 10<sup>4</sup></code>
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.php b/src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.php
new file mode 100644
index 0000000..e7b8146
--- /dev/null
+++ b/src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.php
@@ -0,0 +1,48 @@
+<?php
+
+namespace leetcode\g0001_0100\s0094_binary_tree_inorder_traversal;
+
+// #Easy #Top_100_Liked_Questions #Top_Interview_Questions #Depth_First_Search #Tree #Binary_Tree
+// #Stack #Data_Structure_I_Day_10_Tree #Udemy_Tree_Stack_Queue #Big_O_Time_O(n)_Space_O(n)
+// #2023_12_10_Time_3_ms_(82.09%)_Space_19.1_MB_(47.76%)
+
+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     public $val = null;
+ *     public $left = null;
+ *     public $right = null;
+ *     function __construct($val = 0, $left = null, $right = null) {
+ *         $this->val = $val;
+ *         $this->left = $left;
+ *         $this->right = $right;
+ *     }
+ * }
+ */
+class Solution {
+    /**
+     * @param TreeNode $root
+     * @return Integer[]
+     */
+    public function inorderTraversal($root) {
+        if ($root == null) {
+            return array();
+        }
+        $answer = array();
+        $this->inorderTraversalLocal($root, $answer);
+        return $answer;
+    }
+
+    function inorderTraversalLocal($root, &$answer) {
+        if ($root == null) {
+            return;
+        }
+        if ($root->left != null) {
+            $this->inorderTraversalLocal($root->left, $answer);
+        }
+        array_push($answer, $root->val);
+        if ($root->right != null) {
+            $this->inorderTraversalLocal($root->right, $answer);
+        }
+    }
+}
diff --git a/src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/readme.md b/src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/readme.md
new file mode 100644
index 0000000..5068d01
--- /dev/null
+++ b/src/main/php/g0001_0100/s0094_binary_tree_inorder_traversal/readme.md
@@ -0,0 +1,48 @@
+94\. Binary Tree Inorder Traversal
+
+Easy
+
+Given the `root` of a binary tree, return _the inorder traversal of its nodes' values_.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/09/15/inorder_1.jpg)
+
+**Input:** root = [1,null,2,3]
+
+**Output:** [1,3,2] 
+
+**Example 2:**
+
+**Input:** root = []
+
+**Output:** [] 
+
+**Example 3:**
+
+**Input:** root = [1]
+
+**Output:** [1] 
+
+**Example 4:**
+
+![](https://assets.leetcode.com/uploads/2020/09/15/inorder_5.jpg)
+
+**Input:** root = [1,2]
+
+**Output:** [2,1] 
+
+**Example 5:**
+
+![](https://assets.leetcode.com/uploads/2020/09/15/inorder_4.jpg)
+
+**Input:** root = [1,null,2]
+
+**Output:** [1,2] 
+
+**Constraints:**
+
+*   The number of nodes in the tree is in the range `[0, 100]`.
+*   `-100 <= Node.val <= 100`
+
+**Follow up:** Recursive solution is trivial, could you do it iteratively?
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0096_unique_binary_search_trees/Solution.php b/src/main/php/g0001_0100/s0096_unique_binary_search_trees/Solution.php
new file mode 100644
index 0000000..0e1d1e1
--- /dev/null
+++ b/src/main/php/g0001_0100/s0096_unique_binary_search_trees/Solution.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace leetcode\g0001_0100\s0096_unique_binary_search_trees;
+
+// #Medium #Top_100_Liked_Questions #Dynamic_Programming #Math #Tree #Binary_Tree
+// #Binary_Search_Tree #Dynamic_Programming_I_Day_11 #Big_O_Time_O(n)_Space_O(1)
+// #2023_12_10_Time_0_ms_(100.00%)_Space_19.1_MB_(44.44%)
+
+class Solution {
+    /**
+     * @param Integer $n
+     * @return Integer
+     */
+    public function numTrees($n) {
+        $result = 1;
+        for ($i = 0; $i < $n; $i++) {
+            $result *= 2 * $n - $i;
+            $result /= $i + 1;
+        }
+        $result /= $n + 1;
+        return (int)$result;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0096_unique_binary_search_trees/readme.md b/src/main/php/g0001_0100/s0096_unique_binary_search_trees/readme.md
new file mode 100644
index 0000000..de6a286
--- /dev/null
+++ b/src/main/php/g0001_0100/s0096_unique_binary_search_trees/readme.md
@@ -0,0 +1,23 @@
+96\. Unique Binary Search Trees
+
+Medium
+
+Given an integer `n`, return _the number of structurally unique **BST'**s (binary search trees) which has exactly_ `n` _nodes of unique values from_ `1` _to_ `n`.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2021/01/18/uniquebstn3.jpg)
+
+**Input:** n = 3
+
+**Output:** 5 
+
+**Example 2:**
+
+**Input:** n = 1
+
+**Output:** 1 
+
+**Constraints:**
+
+*   `1 <= n <= 19`
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0098_validate_binary_search_tree/Solution.php b/src/main/php/g0001_0100/s0098_validate_binary_search_tree/Solution.php
new file mode 100644
index 0000000..c135671
--- /dev/null
+++ b/src/main/php/g0001_0100/s0098_validate_binary_search_tree/Solution.php
@@ -0,0 +1,41 @@
+<?php
+
+namespace leetcode\g0001_0100\s0098_validate_binary_search_tree;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Depth_First_Search #Tree #Binary_Tree
+// #Binary_Search_Tree #Data_Structure_I_Day_14_Tree #Level_1_Day_8_Binary_Search_Tree
+// #Udemy_Tree_Stack_Queue #Big_O_Time_O(N)_Space_O(log(N))
+// #2023_12_10_Time_10_ms_(70.97%)_Space_21.7_MB_(58.06%)
+
+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     public $val = null;
+ *     public $left = null;
+ *     public $right = null;
+ *     function __construct($val = 0, $left = null, $right = null) {
+ *         $this->val = $val;
+ *         $this->left = $left;
+ *         $this->right = $right;
+ *     }
+ * }
+ */
+class Solution {
+    /**
+     * @param TreeNode $root
+     * @return Boolean
+     */
+    public function isValidBST($root) {
+        return $this->solve($root, PHP_INT_MIN, PHP_INT_MAX);
+    }
+
+    private function solve($root, $left, $right) {
+        if ($root == null) {
+            return true;
+        }
+        if ($root->val <= $left || $root->val >= $right) {
+            return false;
+        }
+        return $this->solve($root->left, $left, $root->val) && $this->solve($root->right, $root->val, $right);
+    }
+}
diff --git a/src/main/php/g0001_0100/s0098_validate_binary_search_tree/readme.md b/src/main/php/g0001_0100/s0098_validate_binary_search_tree/readme.md
new file mode 100644
index 0000000..a65734a
--- /dev/null
+++ b/src/main/php/g0001_0100/s0098_validate_binary_search_tree/readme.md
@@ -0,0 +1,34 @@
+98\. Validate Binary Search Tree
+
+Medium
+
+Given the `root` of a binary tree, _determine if it is a valid binary search tree (BST)_.
+
+A **valid BST** is defined as follows:
+
+*   The left subtree of a node contains only nodes with keys **less than** the node's key.
+*   The right subtree of a node contains only nodes with keys **greater than** the node's key.
+*   Both the left and right subtrees must also be binary search trees.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/12/01/tree1.jpg)
+
+**Input:** root = [2,1,3]
+
+**Output:** true 
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2020/12/01/tree2.jpg)
+
+**Input:** root = [5,1,4,null,null,3,6]
+
+**Output:** false
+
+**Explanation:** The root node's value is 5 but its right child's value is 4. 
+
+**Constraints:**
+
+*   The number of nodes in the tree is in the range <code>[1, 10<sup>4</sup>]</code>.
+*   <code>-2<sup>31</sup> <= Node.val <= 2<sup>31</sup> - 1</code>
\ No newline at end of file
diff --git a/src/test/php/g0001_0100/s0073_set_matrix_zeroes/SolutionTest.php b/src/test/php/g0001_0100/s0073_set_matrix_zeroes/SolutionTest.php
new file mode 100644
index 0000000..f0d6a4d
--- /dev/null
+++ b/src/test/php/g0001_0100/s0073_set_matrix_zeroes/SolutionTest.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace leetcode\g0001_0100\s0073_set_matrix_zeroes;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testSetZeroes() {
+        $matrix = [[1, 1, 1], [1, 0, 1], [1, 1, 1]];
+        $solution = new Solution();
+        $solution->setZeroes($matrix);
+        $this->assertEquals([[1, 0, 1], [0, 0, 0], [1, 0, 1]], $matrix);
+    }
+
+    public function testSetZeroes2() {
+        $matrix = [[0, 1, 2, 0], [3, 4, 5, 2], [1, 3, 1, 5]];
+        $solution = new Solution();
+        $solution->setZeroes($matrix);
+        $this->assertEquals([[0, 0, 0, 0], [0, 4, 5, 0], [0, 3, 1, 0]], $matrix);
+    }
+}
diff --git a/src/test/php/g0001_0100/s0074_search_a_2d_matrix/SolutionTest.php b/src/test/php/g0001_0100/s0074_search_a_2d_matrix/SolutionTest.php
new file mode 100644
index 0000000..e343a5a
--- /dev/null
+++ b/src/test/php/g0001_0100/s0074_search_a_2d_matrix/SolutionTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace leetcode\g0001_0100\s0074_search_a_2d_matrix;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testSearchMatrix() {
+        $input = [[1, 3, 5, 7], [10, 11, 16, 20], [23, 30, 34, 60]];
+        $solution = new Solution();
+        $this->assertEquals(true, $solution->searchMatrix($input, 3));
+    }
+
+    public function testSearchMatrix2() {
+        $input = [[1, 3, 5, 7], [10, 11, 16, 20], [23, 30, 34, 60]];
+        $solution = new Solution();
+        $this->assertEquals(false, $solution->searchMatrix($input, 13));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0075_sort_colors/SolutionTest.php b/src/test/php/g0001_0100/s0075_sort_colors/SolutionTest.php
new file mode 100644
index 0000000..862a3e2
--- /dev/null
+++ b/src/test/php/g0001_0100/s0075_sort_colors/SolutionTest.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace leetcode\g0001_0100\s0075_sort_colors;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testSortColors() {
+        $array = [2, 0, 2, 1, 1, 0];
+        $solution = new Solution();
+        $solution->sortColors($array);
+        $this->assertEquals([0, 0, 1, 1, 2, 2], $array);
+    }
+
+    public function testSortColors2() {
+        $array = [2, 0, 1];
+        $solution = new Solution();
+        $solution->sortColors($array);
+        $this->assertEquals([0, 1, 2], $array);
+    }
+}
diff --git a/src/test/php/g0001_0100/s0076_minimum_window_substring/SolutionTest.php b/src/test/php/g0001_0100/s0076_minimum_window_substring/SolutionTest.php
new file mode 100644
index 0000000..1eb610f
--- /dev/null
+++ b/src/test/php/g0001_0100/s0076_minimum_window_substring/SolutionTest.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace leetcode\g0001_0100\s0076_minimum_window_substring;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testMinWindow() {
+        $solution = new Solution();
+        $this->assertEquals("BANC", $solution->minWindow("ADOBECODEBANC", "ABC"));
+    }
+
+    public function testMinWindow2() {
+        $solution = new Solution();
+        $this->assertEquals("a", $solution->minWindow("a", "a"));
+    }
+
+    public function testMinWindow3() {
+        $solution = new Solution();
+        $this->assertEquals("", $solution->minWindow("a", "aa"));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0078_subsets/SolutionTest.php b/src/test/php/g0001_0100/s0078_subsets/SolutionTest.php
new file mode 100644
index 0000000..067a7f3
--- /dev/null
+++ b/src/test/php/g0001_0100/s0078_subsets/SolutionTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace leetcode\g0001_0100\s0078_subsets;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testSubsets() {
+        $expected = [[], [1], [1, 2], [1, 2, 3], [1, 3], [2], [2, 3], [3]];
+        $solution = new Solution();
+        $this->assertEquals($expected, $solution->subsets([1, 2, 3]));
+    }
+
+    public function testSubsets2() {
+        $expected = [[], [0]];
+        $solution = new Solution();
+        $this->assertEquals($expected, $solution->subsets([0]));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0079_word_search/SolutionTest.php b/src/test/php/g0001_0100/s0079_word_search/SolutionTest.php
new file mode 100644
index 0000000..4cdc49e
--- /dev/null
+++ b/src/test/php/g0001_0100/s0079_word_search/SolutionTest.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace leetcode\g0001_0100\s0079_word_search;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testExist() {
+        $input = [['A', 'B', 'C', 'E'], ['S', 'F', 'C', 'S'], ['A', 'D', 'E', 'E']];
+        $solution = new Solution();
+        $this->assertEquals(true, $solution->exist($input, "ABCCED"));
+    }
+
+    public function testExist2() {
+        $input = [['A', 'B', 'C', 'E'], ['S', 'F', 'C', 'S'], ['A', 'D', 'E', 'E']];
+        $solution = new Solution();
+        $this->assertEquals(true, $solution->exist($input, "SEE"));
+    }
+
+    public function testExist3() {
+        $input = [['A', 'B', 'C', 'E'], ['S', 'F', 'C', 'S'], ['A', 'D', 'E', 'E']];
+        $solution = new Solution();
+        $this->assertEquals(false, $solution->exist($input, "ABCB"));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0084_largest_rectangle_in_histogram/SolutionTest.php b/src/test/php/g0001_0100/s0084_largest_rectangle_in_histogram/SolutionTest.php
new file mode 100644
index 0000000..36fd60e
--- /dev/null
+++ b/src/test/php/g0001_0100/s0084_largest_rectangle_in_histogram/SolutionTest.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace leetcode\g0001_0100\s0084_largest_rectangle_in_histogram;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testLargestRectangleArea() {
+        $solution = new Solution();
+        $this->assertEquals(10, $solution->largestRectangleArea([2, 1, 5, 6, 2, 3]));
+    }
+
+    public function testLargestRectangleArea2() {
+        $solution = new Solution();
+        $this->assertEquals(4, $solution->largestRectangleArea([2, 4]));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0094_binary_tree_inorder_traversal/SolutionTest.php b/src/test/php/g0001_0100/s0094_binary_tree_inorder_traversal/SolutionTest.php
new file mode 100644
index 0000000..b3c5414
--- /dev/null
+++ b/src/test/php/g0001_0100/s0094_binary_tree_inorder_traversal/SolutionTest.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace leetcode\g0001_0100\s0094_binary_tree_inorder_traversal;
+
+use leetcode\com_github_leetcode\TreeNode;
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testInorderTraversal() {
+        $treeNode = new TreeNode(1);
+        $treeNode2 = new TreeNode(2);
+        $treeNode->right = $treeNode2;
+        $treeNode2->left = new TreeNode(3);
+        $solution = new Solution();
+        $this->assertEquals("[1,3,2]", json_encode($solution->inorderTraversal($treeNode)));
+    }
+
+    public function testInorderTraversal2() {
+        $solution = new Solution();
+        $this->assertEquals("[]", json_encode($solution->inorderTraversal(null)));
+    }
+
+    public function testInorderTraversal3() {
+        $solution = new Solution();
+        $this->assertEquals("[1]", json_encode($solution->inorderTraversal(new TreeNode(1))));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0096_unique_binary_search_trees/SolutionTest.php b/src/test/php/g0001_0100/s0096_unique_binary_search_trees/SolutionTest.php
new file mode 100644
index 0000000..6d625be
--- /dev/null
+++ b/src/test/php/g0001_0100/s0096_unique_binary_search_trees/SolutionTest.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace leetcode\g0001_0100\s0096_unique_binary_search_trees;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testNumTrees() {
+        $solution = new Solution();
+        $this->assertEquals(5, $solution->numTrees(3));
+    }
+
+    public function testNumTrees2() {
+        $solution = new Solution();
+        $this->assertEquals(1, $solution->numTrees(1));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0098_validate_binary_search_tree/SolutionTest.php b/src/test/php/g0001_0100/s0098_validate_binary_search_tree/SolutionTest.php
new file mode 100644
index 0000000..0052fd9
--- /dev/null
+++ b/src/test/php/g0001_0100/s0098_validate_binary_search_tree/SolutionTest.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace leetcode\g0001_0100\s0098_validate_binary_search_tree;
+
+use leetcode\com_github_leetcode\TreeNode;
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testIsValidBST() {
+        $treeNode1 = new TreeNode(2);
+        $treeNode1->left = new TreeNode(1);
+        $treeNode1->right = new TreeNode(3);
+        $solution = new Solution();
+        $this->assertEquals(true, $solution->isValidBST($treeNode1));
+    }
+
+    public function testIsValidBST2() {
+        $treeNode = new TreeNode(5);
+        $treeNode->left = new TreeNode(1);
+        $treeNode->right = new TreeNode(4);
+        $treeNode->right->left = new TreeNode(3);
+        $treeNode->right->right = new TreeNode(6);
+        $solution = new Solution();
+        $this->assertEquals(false, $solution->isValidBST($treeNode));
+    }
+}