diff --git a/README.md b/README.md
index fab7185..94f91a0 100644
--- a/README.md
+++ b/README.md
@@ -212,6 +212,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0198 |[House Robber](src/main/php/g0101_0200/s0198_house_robber/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Big_O_Time_O(n)_Space_O(n) | 4 | 64.29
 
 #### Day 4
 
@@ -287,6 +288,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
 | 0064 |[Minimum Path Sum](src/main/php/g0001_0100/s0064_minimum_path_sum/Solution.php)| Medium | Top_100_Liked_Questions, Array, Dynamic_Programming, Matrix, Big_O_Time_O(m\*n)_Space_O(m\*n) | 20 | 81.48
+| 0221 |[Maximal Square](src/main/php/g0201_0300/s0221_maximal_square/Solution.php)| Medium | Top_100_Liked_Questions, Array, Dynamic_Programming, Matrix, Big_O_Time_O(m\*n)_Space_O(m\*n) | 209 | 83.33
 
 #### Day 17
 
@@ -491,6 +493,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0200 |[Number of Islands](src/main/php/g0101_0200/s0200_number_of_islands/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Depth_First_Search, Breadth_First_Search, Matrix, Union_Find, Big_O_Time_O(M\*N)_Space_O(M\*N) | 97 | 82.05
 
 #### Day 2 Matrix Related Problems
 
@@ -626,6 +629,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
 | 0021 |[Merge Two Sorted Lists](src/main/php/g0001_0100/s0021_merge_two_sorted_lists/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Linked_List, Recursion, Big_O_Time_O(m+n)_Space_O(m+n) | 3 | 90.57
+| 0206 |[Reverse Linked List](src/main/php/g0201_0300/s0206_reverse_linked_list/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Linked_List, Recursion, Big_O_Time_O(N)_Space_O(1) | 0 | 100.00
 
 #### Day 4 Linked List
 
@@ -660,6 +664,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0200 |[Number of Islands](src/main/php/g0101_0200/s0200_number_of_islands/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Depth_First_Search, Breadth_First_Search, Matrix, Union_Find, Big_O_Time_O(M\*N)_Space_O(M\*N) | 97 | 82.05
 
 #### Day 10 Dynamic Programming
 
@@ -727,6 +732,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0226 |[Invert Binary Tree](src/main/php/g0201_0300/s0226_invert_binary_tree/Solution.php)| Easy | Top_100_Liked_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(n)_Space_O(n) | 6 | 62.79
 
 #### Day 7 Tree
 
@@ -759,6 +765,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0198 |[House Robber](src/main/php/g0101_0200/s0198_house_robber/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Big_O_Time_O(n)_Space_O(n) | 4 | 64.29
 
 #### Day 13 Dynamic Programming
 
@@ -784,6 +791,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
 | 0155 |[Min Stack](src/main/php/g0101_0200/s0155_min_stack/MinStack.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Stack, Design, Big_O_Time_O(1)_Space_O(N) | 19 | 100.00
+| 0208 |[Implement Trie (Prefix Tree)](src/main/php/g0201_0300/s0208_implement_trie_prefix_tree/Trie.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Hash_Table, Design, Trie, Big_O_Time_O(word.length())_or_O(prefix.length())_Space_O(N) | 83 | 46.67
 
 #### Day 17 Interval
 
@@ -840,6 +848,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 |-|-|-|-|-|-
 | 0121 |[Best Time to Buy and Sell Stock](src/main/php/g0101_0200/s0121_best_time_to_buy_and_sell_stock/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Big_O_Time_O(N)_Space_O(1) | 282 | 43.99
 | 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
+| 0189 |[Rotate Array](src/main/php/g0101_0200/s0189_rotate_array/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Math, Two_Pointers, Big_O_Time_O(n)_Space_O(1) | 60 | 67.03
 | 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
@@ -856,6 +865,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
 | 0053 |[Maximum Subarray](src/main/php/g0001_0100/s0053_maximum_subarray/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Divide_and_Conquer, Big_O_Time_O(n)_Space_O(1) | 185 | 95.51
+| 0169 |[Majority Element](src/main/php/g0101_0200/s0169_majority_element/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Sorting, Counting, Divide_and_Conquer, Big_O_Time_O(n)_Space_O(1) | 43 | 72.03
 
 #### Udemy Sorting Algorithms
 
@@ -879,6 +889,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 | 0024 |[Swap Nodes in Pairs](src/main/php/g0001_0100/s0024_swap_nodes_in_pairs/Solution.php)| Medium | Top_100_Liked_Questions, Linked_List, Recursion, Big_O_Time_O(n)_Space_O(1) | 3 | 85.71
 | 0142 |[Linked List Cycle II](src/main/php/g0101_0200/s0142_linked_list_cycle_ii/Solution.php)| Medium | Top_100_Liked_Questions, Hash_Table, Two_Pointers, Linked_List, Big_O_Time_O(N)_Space_O(1) | 7 | 100.00
 | 0141 |[Linked List Cycle](src/main/php/g0101_0200/s0141_linked_list_cycle/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Hash_Table, Two_Pointers, Linked_List, Big_O_Time_O(N)_Space_O(1) | 8 | 90.60
+| 0206 |[Reverse Linked List](src/main/php/g0201_0300/s0206_reverse_linked_list/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Linked_List, Recursion, Big_O_Time_O(N)_Space_O(1) | 0 | 100.00
 | 0021 |[Merge Two Sorted Lists](src/main/php/g0001_0100/s0021_merge_two_sorted_lists/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Linked_List, Recursion, Big_O_Time_O(m+n)_Space_O(m+n) | 3 | 90.57
 | 0160 |[Intersection of Two Linked Lists](src/main/php/g0101_0200/s0160_intersection_of_two_linked_lists/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Hash_Table, Two_Pointers, Linked_List, Big_O_Time_O(M+N)_Space_O(1) | 30 | 81.67
 | 0138 |[Copy List with Random Pointer](src/main/php/g0101_0200/s0138_copy_list_with_random_pointer/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Hash_Table, Linked_List, Big_O_Time_O(N)_Space_O(N) | 2300 | 60.00
@@ -891,6 +902,7 @@ 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
 | 0102 |[Binary Tree Level Order Traversal](src/main/php/g0101_0200/s0102_binary_tree_level_order_traversal/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(N) | 4 | 96.08
+| 0226 |[Invert Binary Tree](src/main/php/g0201_0300/s0226_invert_binary_tree/Solution.php)| Easy | Top_100_Liked_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(n)_Space_O(n) | 6 | 62.79
 | 0104 |[Maximum Depth of Binary Tree](src/main/php/g0101_0200/s0104_maximum_depth_of_binary_tree/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(H) | 9 | 63.06
 | 0124 |[Binary Tree Maximum Path Sum](src/main/php/g0101_0200/s0124_binary_tree_maximum_path_sum/Solution.php)| Hard | Top_100_Liked_Questions, Top_Interview_Questions, Dynamic_Programming, Depth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(N) | 16 | 100.00
 | 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
@@ -899,11 +911,13 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0208 |[Implement Trie (Prefix Tree)](src/main/php/g0201_0300/s0208_implement_trie_prefix_tree/Trie.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Hash_Table, Design, Trie, Big_O_Time_O(word.length())_or_O(prefix.length())_Space_O(N) | 83 | 46.67
 
 #### Udemy Graph
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0200 |[Number of Islands](src/main/php/g0101_0200/s0200_number_of_islands/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Depth_First_Search, Breadth_First_Search, Matrix, Union_Find, Big_O_Time_O(M\*N)_Space_O(M\*N) | 97 | 82.05
 
 #### Udemy Dynamic Programming
 
@@ -911,6 +925,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 |-|-|-|-|-|-
 | 0139 |[Word Break](src/main/php/g0101_0200/s0139_word_break/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Hash_Table, Dynamic_Programming, Trie, Memoization, Big_O_Time_O(M+max\*N)_Space_O(M+N+max) | 7 | 75.00
 | 0152 |[Maximum Product Subarray](src/main/php/g0101_0200/s0152_maximum_product_subarray/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Big_O_Time_O(N)_Space_O(1) | 15 | 92.86
+| 0198 |[House Robber](src/main/php/g0101_0200/s0198_house_robber/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Big_O_Time_O(n)_Space_O(n) | 4 | 64.29
 | 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, 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, Big_O_Time_O(m\*n)_Space_O(m\*n) | 20 | 81.48
 | 0072 |[Edit Distance](src/main/php/g0001_0100/s0072_edit_distance/Solution.php)| Hard | Top_100_Liked_Questions, String, Dynamic_Programming, Big_O_Time_O(n^2)_Space_O(n2) | 29 | 75.00
@@ -984,6 +999,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0206 |[Reverse Linked List](src/main/php/g0201_0300/s0206_reverse_linked_list/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Linked_List, Recursion, Big_O_Time_O(N)_Space_O(1) | 0 | 100.00
 
 #### Day 9 Stack Queue
 
@@ -1009,6 +1025,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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+| 0226 |[Invert Binary Tree](src/main/php/g0201_0300/s0226_invert_binary_tree/Solution.php)| Easy | Top_100_Liked_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(n)_Space_O(n) | 6 | 62.79
 
 #### Day 13 Tree
 
@@ -1028,6 +1045,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
 | 0136 |[Single Number](src/main/php/g0101_0200/s0136_single_number/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Bit_Manipulation, Big_O_Time_O(N)_Space_O(1) | 33 | 80.08
+| 0169 |[Majority Element](src/main/php/g0101_0200/s0169_majority_element/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Sorting, Counting, Divide_and_Conquer, Big_O_Time_O(n)_Space_O(1) | 43 | 72.03
 | 0015 |[3Sum](src/main/php/g0001_0100/s0015_3sum/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Sorting, Two_Pointers, Big_O_Time_O(n^2)_Space_O(1), Big_O_Time_O(n\*log(n))_Space_O(n^2) | 252 | 77.94
 
 #### Day 2 Array
@@ -1136,6 +1154,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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+| 0215 |[Kth Largest Element in an Array](src/main/php/g0201_0300/s0215_kth_largest_element_in_an_array/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Sorting, Heap_Priority_Queue, Divide_and_Conquer, Quickselect, Big_O_Time_O(n\*log(n))_Space_O(log(n)) | 222 | 49.15
 
 #### Day 21 Heap Priority Queue
 
@@ -1154,6 +1173,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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+| 0189 |[Rotate Array](src/main/php/g0101_0200/s0189_rotate_array/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Math, Two_Pointers, Big_O_Time_O(n)_Space_O(1) | 60 | 67.03
 
 #### Day 3 Two Pointers
 
@@ -1197,6 +1217,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
 | 0021 |[Merge Two Sorted Lists](src/main/php/g0001_0100/s0021_merge_two_sorted_lists/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Linked_List, Recursion, Big_O_Time_O(m+n)_Space_O(m+n) | 3 | 90.57
+| 0206 |[Reverse Linked List](src/main/php/g0201_0300/s0206_reverse_linked_list/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Linked_List, Recursion, Big_O_Time_O(N)_Space_O(1) | 0 | 100.00
 
 #### Day 11 Recursion Backtracking
 
@@ -1209,6 +1230,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
 | 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, Big_O_Time_O(n)_Space_O(n) | 3 | 82.81
+| 0198 |[House Robber](src/main/php/g0101_0200/s0198_house_robber/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Big_O_Time_O(n)_Space_O(n) | 4 | 64.29
 
 #### Day 13 Bit Manipulation
 
@@ -1258,6 +1280,7 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
+| 0200 |[Number of Islands](src/main/php/g0101_0200/s0200_number_of_islands/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Depth_First_Search, Breadth_First_Search, Matrix, Union_Find, Big_O_Time_O(M\*N)_Space_O(M\*N) | 97 | 82.05
 
 #### Day 7 Breadth First Search Depth First Search
 
@@ -1349,6 +1372,16 @@ Php-based LeetCode algorithm problem solutions, regularly updated.
 
 | #    |      Title     | Difficulty  | Tag         | Time, ms | Time, %
 |------|----------------|-------------|-------------|----------|---------
+| 0226 |[Invert Binary Tree](src/main/php/g0201_0300/s0226_invert_binary_tree/Solution.php)| Easy | Top_100_Liked_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Data_Structure_I_Day_12_Tree, Level_2_Day_6_Tree, Udemy_Tree_Stack_Queue, Big_O_Time_O(n)_Space_O(n) | 6 | 62.79
+| 0221 |[Maximal Square](src/main/php/g0201_0300/s0221_maximal_square/Solution.php)| Medium | Top_100_Liked_Questions, Array, Dynamic_Programming, Matrix, Dynamic_Programming_I_Day_16, Big_O_Time_O(m\*n)_Space_O(m\*n) | 209 | 83.33
+| 0215 |[Kth Largest Element in an Array](src/main/php/g0201_0300/s0215_kth_largest_element_in_an_array/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Sorting, Heap_Priority_Queue, Divide_and_Conquer, Quickselect, Data_Structure_II_Day_20_Heap_Priority_Queue, Big_O_Time_O(n\*log(n))_Space_O(log(n)) | 222 | 49.15
+| 0208 |[Implement Trie (Prefix Tree)](src/main/php/g0201_0300/s0208_implement_trie_prefix_tree/Trie.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Hash_Table, Design, Trie, Level_2_Day_16_Design, Udemy_Trie_and_Heap, Big_O_Time_O(word.length())_or_O(prefix.length())_Space_O(N) | 83 | 46.67
+| 0207 |[Course Schedule](src/main/php/g0201_0300/s0207_course_schedule/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Breadth_First_Search, Graph, Topological_Sort, Big_O_Time_O(N)_Space_O(N) | 25 | 89.29
+| 0206 |[Reverse Linked List](src/main/php/g0201_0300/s0206_reverse_linked_list/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Linked_List, Recursion, Data_Structure_I_Day_8_Linked_List, Algorithm_I_Day_10_Recursion_Backtracking, Level_1_Day_3_Linked_List, Udemy_Linked_List, Big_O_Time_O(N)_Space_O(1) | 0 | 100.00
+| 0200 |[Number of Islands](src/main/php/g0101_0200/s0200_number_of_islands/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Depth_First_Search, Breadth_First_Search, Matrix, Union_Find, Algorithm_II_Day_6_Breadth_First_Search_Depth_First_Search, Graph_Theory_I_Day_1_Matrix_Related_Problems, Level_1_Day_9_Graph/BFS/DFS, Udemy_Graph, Big_O_Time_O(M\*N)_Space_O(M\*N) | 97 | 82.05
+| 0198 |[House Robber](src/main/php/g0101_0200/s0198_house_robber/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Algorithm_I_Day_12_Dynamic_Programming, Dynamic_Programming_I_Day_3, Level_2_Day_12_Dynamic_Programming, Udemy_Dynamic_Programming, Big_O_Time_O(n)_Space_O(n) | 4 | 64.29
+| 0189 |[Rotate Array](src/main/php/g0101_0200/s0189_rotate_array/Solution.php)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Math, Two_Pointers, Algorithm_I_Day_2_Two_Pointers, Udemy_Arrays, Big_O_Time_O(n)_Space_O(1) | 60 | 67.03
+| 0169 |[Majority Element](src/main/php/g0101_0200/s0169_majority_element/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Sorting, Counting, Divide_and_Conquer, Data_Structure_II_Day_1_Array, Udemy_Famous_Algorithm, Big_O_Time_O(n)_Space_O(1) | 43 | 72.03
 | 0160 |[Intersection of Two Linked Lists](src/main/php/g0101_0200/s0160_intersection_of_two_linked_lists/Solution.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Hash_Table, Two_Pointers, Linked_List, Data_Structure_II_Day_11_Linked_List, Udemy_Linked_List, Big_O_Time_O(M+N)_Space_O(1) | 30 | 81.67
 | 0155 |[Min Stack](src/main/php/g0101_0200/s0155_min_stack/MinStack.php)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Stack, Design, Data_Structure_II_Day_14_Stack_Queue, Programming_Skills_II_Day_18, Level_2_Day_16_Design, Udemy_Design, Big_O_Time_O(1)_Space_O(N) | 19 | 100.00
 | 0153 |[Find Minimum in Rotated Sorted Array](src/main/php/g0101_0200/s0153_find_minimum_in_rotated_sorted_array/Solution.php)| Medium | Top_100_Liked_Questions, Array, Binary_Search, Algorithm_II_Day_2_Binary_Search, Binary_Search_I_Day_12, Udemy_Binary_Search, Big_O_Time_O(log_N)_Space_O(log_N) | 9 | 73.47
diff --git a/src/main/php/g0101_0200/s0169_majority_element/Solution.php b/src/main/php/g0101_0200/s0169_majority_element/Solution.php
new file mode 100644
index 0000000..79d7255
--- /dev/null
+++ b/src/main/php/g0101_0200/s0169_majority_element/Solution.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace leetcode\g0101_0200\s0169_majority_element;
+
+// #Easy #Top_100_Liked_Questions #Top_Interview_Questions #Array #Hash_Table #Sorting #Counting
+// #Divide_and_Conquer #Data_Structure_II_Day_1_Array #Udemy_Famous_Algorithm
+// #Big_O_Time_O(n)_Space_O(1) #2023_12_21_Time_43_ms_(72.03%)_Space_23_MB_(100.00%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer
+     */
+    public function majorityElement($nums) {
+        $search = array_count_values($nums);
+        $count = count($nums) / 2;
+        foreach ($search as $key => $value) {
+            if ($value > $count) {
+                return $key;
+            }
+        }
+    }
+}
diff --git a/src/main/php/g0101_0200/s0169_majority_element/readme.md b/src/main/php/g0101_0200/s0169_majority_element/readme.md
new file mode 100644
index 0000000..5ea5071
--- /dev/null
+++ b/src/main/php/g0101_0200/s0169_majority_element/readme.md
@@ -0,0 +1,27 @@
+169\. Majority Element
+
+Easy
+
+Given an array `nums` of size `n`, return _the majority element_.
+
+The majority element is the element that appears more than `⌊n / 2⌋` times. You may assume that the majority element always exists in the array.
+
+**Example 1:**
+
+**Input:** nums = [3,2,3]
+
+**Output:** 3 
+
+**Example 2:**
+
+**Input:** nums = [2,2,1,1,1,2,2]
+
+**Output:** 2 
+
+**Constraints:**
+
+*   `n == nums.length`
+*   <code>1 <= n <= 5 * 10<sup>4</sup></code>
+*   <code>-2<sup>31</sup> <= nums[i] <= 2<sup>31</sup> - 1</code>
+
+**Follow-up:** Could you solve the problem in linear time and in `O(1)` space?
\ No newline at end of file
diff --git a/src/main/php/g0101_0200/s0189_rotate_array/Solution.php b/src/main/php/g0101_0200/s0189_rotate_array/Solution.php
new file mode 100644
index 0000000..c905267
--- /dev/null
+++ b/src/main/php/g0101_0200/s0189_rotate_array/Solution.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace leetcode\g0101_0200\s0189_rotate_array;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Math #Two_Pointers
+// #Algorithm_I_Day_2_Two_Pointers #Udemy_Arrays #Big_O_Time_O(n)_Space_O(1)
+// #2023_12_21_Time_60_ms_(67.03%)_Space_27.9_MB_(100.00%)
+
+class Solution {
+    private function reverse(&$nums, $l, $r) {
+        while ($l <= $r) {
+            $temp = $nums[$l];
+            $nums[$l] = $nums[$r];
+            $nums[$r] = $temp;
+            $l++;
+            $r--;
+        }
+    }
+
+    /**
+     * @param Integer[] $nums
+     * @param Integer $k
+     * @return NULL
+     */
+    public function rotate(&$nums, $k) {
+        $n = count($nums);
+        $t = $n - ($k % $n);
+        $this->reverse($nums, 0, $t - 1);
+        $this->reverse($nums, $t, $n - 1);
+        $this->reverse($nums, 0, $n - 1);
+    }
+}
diff --git a/src/main/php/g0101_0200/s0189_rotate_array/readme.md b/src/main/php/g0101_0200/s0189_rotate_array/readme.md
new file mode 100644
index 0000000..390f269
--- /dev/null
+++ b/src/main/php/g0101_0200/s0189_rotate_array/readme.md
@@ -0,0 +1,39 @@
+189\. Rotate Array
+
+Medium
+
+Given an array, rotate the array to the right by `k` steps, where `k` is non-negative.
+
+**Example 1:**
+
+**Input:** nums = [1,2,3,4,5,6,7], k = 3
+
+**Output:** [5,6,7,1,2,3,4]
+
+**Explanation:**
+
+    rotate 1 steps to the right: [7,1,2,3,4,5,6]
+    rotate 2 steps to the right: [6,7,1,2,3,4,5]
+    rotate 3 steps to the right: [5,6,7,1,2,3,4] 
+
+**Example 2:**
+
+**Input:** nums = [-1,-100,3,99], k = 2
+
+**Output:** [3,99,-1,-100]
+
+**Explanation:**
+
+    rotate 1 steps to the right: [99,-1,-100,3]
+    rotate 2 steps to the right: [3,99,-1,-100] 
+
+**Constraints:**
+
+*   <code>1 <= nums.length <= 10<sup>5</sup></code>
+*   <code>-2<sup>31</sup> <= nums[i] <= 2<sup>31</sup> - 1</code>
+*   <code>0 <= k <= 10<sup>5</sup></code>
+
+**Follow up:**
+
+*   Try to come up with as many solutions as you can. There are at least **three** different ways to solve this problem.
+*   Could you do it in-place with `O(1)` extra space?
\ No newline at end of file
diff --git a/src/main/php/g0101_0200/s0198_house_robber/Solution.php b/src/main/php/g0101_0200/s0198_house_robber/Solution.php
new file mode 100644
index 0000000..0aca987
--- /dev/null
+++ b/src/main/php/g0101_0200/s0198_house_robber/Solution.php
@@ -0,0 +1,34 @@
+<?php
+
+namespace leetcode\g0101_0200\s0198_house_robber;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Dynamic_Programming
+// #Algorithm_I_Day_12_Dynamic_Programming #Dynamic_Programming_I_Day_3
+// #Level_2_Day_12_Dynamic_Programming #Udemy_Dynamic_Programming #Big_O_Time_O(n)_Space_O(n)
+// #2023_12_21_Time_4_ms_(64.29%)_Space_19.8_MB_(9.52%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer
+     */
+    public function rob($nums) {
+        $n = count($nums);
+        if ($n == 0) {
+            return 0;
+        }
+        if ($n == 1) {
+            return $nums[0];
+        }
+        if ($n == 2) {
+            return max($nums[0], $nums[1]);
+        }
+        $profit = array();
+        $profit[0] = $nums[0];
+        $profit[1] = max($nums[1], $nums[0]);
+        for ($i = 2; $i < $n; $i++) {
+            $profit[$i] = max($profit[$i - 1], $nums[$i] + $profit[$i - 2]);
+        }
+        return $profit[$n - 1];
+    }
+}
diff --git a/src/main/php/g0101_0200/s0198_house_robber/readme.md b/src/main/php/g0101_0200/s0198_house_robber/readme.md
new file mode 100644
index 0000000..4a93a57
--- /dev/null
+++ b/src/main/php/g0101_0200/s0198_house_robber/readme.md
@@ -0,0 +1,34 @@
+198\. House Robber
+
+Medium
+
+You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and **it will automatically contact the police if two adjacent houses were broken into on the same night**.
+
+Given an integer array `nums` representing the amount of money of each house, return _the maximum amount of money you can rob tonight **without alerting the police**_.
+
+**Example 1:**
+
+**Input:** nums = [1,2,3,1]
+
+**Output:** 4
+
+**Explanation:**
+
+    Rob house 1 (money = 1) and then rob house 3 (money = 3).
+    Total amount you can rob = 1 + 3 = 4. 
+
+**Example 2:**
+
+**Input:** nums = [2,7,9,3,1]
+
+**Output:** 12
+
+**Explanation:**
+
+    Rob house 1 (money = 2), rob house 3 (money = 9) and rob house 5 (money = 1).
+    Total amount you can rob = 2 + 9 + 1 = 12. 
+
+**Constraints:**
+
+*   `1 <= nums.length <= 100`
+*   `0 <= nums[i] <= 400`
\ No newline at end of file
diff --git a/src/main/php/g0101_0200/s0200_number_of_islands/Solution.php b/src/main/php/g0101_0200/s0200_number_of_islands/Solution.php
new file mode 100644
index 0000000..2a3b34b
--- /dev/null
+++ b/src/main/php/g0101_0200/s0200_number_of_islands/Solution.php
@@ -0,0 +1,41 @@
+<?php
+
+namespace leetcode\g0101_0200\s0200_number_of_islands;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Depth_First_Search
+// #Breadth_First_Search #Matrix #Union_Find
+// #Algorithm_II_Day_6_Breadth_First_Search_Depth_First_Search
+// #Graph_Theory_I_Day_1_Matrix_Related_Problems #Level_1_Day_9_Graph/BFS/DFS #Udemy_Graph
+// #Big_O_Time_O(M*N)_Space_O(M*N) #2023_12_21_Time_97_ms_(82.05%)_Space_35.3_MB_(100.00%)
+
+class Solution {
+    /**
+     * @param String[][] $grid
+     * @return Integer
+     */
+    public function numIslands($grid) {
+        $islands = 0;
+        if ($grid != null && !empty($grid) && count($grid[0]) != 0) {
+            for ($i = 0; $i < count($grid); $i++) {
+                for ($j = 0; $j < count($grid[0]); $j++) {
+                    if ($grid[$i][$j] == '1') {
+                        $this->dfs($grid, $i, $j);
+                        $islands++;
+                    }
+                }
+            }
+        }
+        return $islands;
+    }
+
+    private function dfs(&$grid, $x, $y) {
+        if ($x < 0 || count($grid) <= $x || $y < 0 || count($grid[0]) <= $y || $grid[$x][$y] != '1') {
+            return;
+        }
+        $grid[$x][$y] = 'x';
+        $this->dfs($grid, $x + 1, $y);
+        $this->dfs($grid, $x - 1, $y);
+        $this->dfs($grid, $x, $y + 1);
+        $this->dfs($grid, $x, $y - 1);
+    }
+}
diff --git a/src/main/php/g0101_0200/s0200_number_of_islands/readme.md b/src/main/php/g0101_0200/s0200_number_of_islands/readme.md
new file mode 100644
index 0000000..0c4292d
--- /dev/null
+++ b/src/main/php/g0101_0200/s0200_number_of_islands/readme.md
@@ -0,0 +1,40 @@
+200\. Number of Islands
+
+Medium
+
+Given an `m x n` 2D binary grid `grid` which represents a map of `'1'`s (land) and `'0'`s (water), return _the number of islands_.
+
+An **island** is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.
+
+**Example 1:**
+
+**Input:**
+
+    grid = [
+      ["1","1","1","1","0"],
+      ["1","1","0","1","0"],
+      ["1","1","0","0","0"],
+      ["0","0","0","0","0"]
+    ]
+
+**Output:** 1 
+
+**Example 2:**
+
+**Input:**
+
+    grid = [
+      ["1","1","0","0","0"],
+      ["1","1","0","0","0"],
+      ["0","0","1","0","0"],
+      ["0","0","0","1","1"]
+    ]
+
+**Output:** 3 
+
+**Constraints:**
+
+*   `m == grid.length`
+*   `n == grid[i].length`
+*   `1 <= m, n <= 300`
+*   `grid[i][j]` is `'0'` or `'1'`.
\ No newline at end of file
diff --git a/src/main/php/g0201_0300/s0206_reverse_linked_list/Solution.php b/src/main/php/g0201_0300/s0206_reverse_linked_list/Solution.php
new file mode 100644
index 0000000..aaae7ea
--- /dev/null
+++ b/src/main/php/g0201_0300/s0206_reverse_linked_list/Solution.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace leetcode\g0201_0300\s0206_reverse_linked_list;
+
+// #Easy #Top_100_Liked_Questions #Top_Interview_Questions #Linked_List #Recursion
+// #Data_Structure_I_Day_8_Linked_List #Algorithm_I_Day_10_Recursion_Backtracking
+// #Level_1_Day_3_Linked_List #Udemy_Linked_List #Big_O_Time_O(N)_Space_O(1)
+// #2023_12_21_Time_0_ms_(100.00%)_Space_20.4_MB_(87.88%)
+
+/**
+ * Definition for a singly-linked list.
+ * class ListNode {
+ *     public $val = 0;
+ *     public $next = null;
+ *     function __construct($val = 0, $next = null) {
+ *         $this->val = $val;
+ *         $this->next = $next;
+ *     }
+ * }
+ */
+class Solution {
+    /**
+     * @param ListNode $head
+     * @return ListNode
+     */
+    public function reverseList($head) {
+        $prev = null;
+        $curr = $head;
+        while ($curr != null) {
+            $next = $curr->next;
+            $curr->next = $prev;
+            $prev = $curr;
+            $curr = $next;
+        }
+        return $prev;
+    }
+}
diff --git a/src/main/php/g0201_0300/s0206_reverse_linked_list/readme.md b/src/main/php/g0201_0300/s0206_reverse_linked_list/readme.md
new file mode 100644
index 0000000..a764d55
--- /dev/null
+++ b/src/main/php/g0201_0300/s0206_reverse_linked_list/readme.md
@@ -0,0 +1,34 @@
+206\. Reverse Linked List
+
+Easy
+
+Given the `head` of a singly linked list, reverse the list, and return _the reversed list_.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2021/02/19/rev1ex1.jpg)
+
+**Input:** head = [1,2,3,4,5]
+
+**Output:** [5,4,3,2,1] 
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2021/02/19/rev1ex2.jpg)
+
+**Input:** head = [1,2]
+
+**Output:** [2,1] 
+
+**Example 3:**
+
+**Input:** head = []
+
+**Output:** [] 
+
+**Constraints:**
+
+*   The number of nodes in the list is the range `[0, 5000]`.
+*   `-5000 <= Node.val <= 5000`
+
+**Follow up:** A linked list can be reversed either iteratively or recursively. Could you implement both?
\ No newline at end of file
diff --git a/src/main/php/g0201_0300/s0207_course_schedule/Solution.php b/src/main/php/g0201_0300/s0207_course_schedule/Solution.php
new file mode 100644
index 0000000..a80ba98
--- /dev/null
+++ b/src/main/php/g0201_0300/s0207_course_schedule/Solution.php
@@ -0,0 +1,46 @@
+<?php
+
+namespace leetcode\g0201_0300\s0207_course_schedule;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Depth_First_Search
+// #Breadth_First_Search #Graph #Topological_Sort #Big_O_Time_O(N)_Space_O(N)
+// #2023_12_21_Time_25_ms_(89.29%)_Space_22.3_MB_(100.00%)
+
+class Solution {
+    const WHITE = 0;
+    const GRAY = 1;
+    const BLACK = 2;
+
+    /**
+     * @param Integer $numCourses
+     * @param Integer[][] $prerequisites
+     * @return Boolean
+     */
+    public function canFinish($numCourses, $prerequisites) {
+        $adj = array_fill(0, $numCourses, []);
+        foreach ($prerequisites as $pre) {
+            array_push($adj[$pre[1]], $pre[0]);
+        }
+        $colors = array_fill(0, $numCourses, self::WHITE);
+        for ($i = 0; $i < $numCourses; $i++) {
+            if ($colors[$i] == self::WHITE && !empty($adj[$i]) && $this->hasCycle($adj, $i, $colors)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private function hasCycle($adj, $node, &$colors) {
+        $colors[$node] = self::GRAY;
+        foreach ($adj[$node] as $nei) {
+            if ($colors[$nei] == self::GRAY) {
+                return true;
+            }
+            if ($colors[$nei] == self::WHITE && $this->hasCycle($adj, $nei, $colors)) {
+                return true;
+            }
+        }
+        $colors[$node] = self::BLACK;
+        return false;
+    }
+}
diff --git a/src/main/php/g0201_0300/s0207_course_schedule/readme.md b/src/main/php/g0201_0300/s0207_course_schedule/readme.md
new file mode 100644
index 0000000..a7b1e9c
--- /dev/null
+++ b/src/main/php/g0201_0300/s0207_course_schedule/readme.md
@@ -0,0 +1,33 @@
+207\. Course Schedule
+
+Medium
+
+There are a total of `numCourses` courses you have to take, labeled from `0` to `numCourses - 1`. You are given an array `prerequisites` where <code>prerequisites[i] = [a<sub>i</sub>, b<sub>i</sub>]</code> indicates that you **must** take course <code>b<sub>i</sub></code> first if you want to take course <code>a<sub>i</sub></code>.
+
+*   For example, the pair `[0, 1]`, indicates that to take course `0` you have to first take course `1`.
+
+Return `true` if you can finish all courses. Otherwise, return `false`.
+
+**Example 1:**
+
+**Input:** numCourses = 2, prerequisites = [[1,0]]
+
+**Output:** true
+
+**Explanation:** There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. 
+
+**Example 2:**
+
+**Input:** numCourses = 2, prerequisites = [[1,0],[0,1]]
+
+**Output:** false
+
+**Explanation:** There are a total of 2 courses to take. To take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible. 
+
+**Constraints:**
+
+*   <code>1 <= numCourses <= 10<sup>5</sup></code>
+*   `0 <= prerequisites.length <= 5000`
+*   `prerequisites[i].length == 2`
+*   <code>0 <= a<sub>i</sub>, b<sub>i</sub> < numCourses</code>
+*   All the pairs prerequisites[i] are **unique**.
\ No newline at end of file
diff --git a/src/main/php/g0201_0300/s0208_implement_trie_prefix_tree/Trie.php b/src/main/php/g0201_0300/s0208_implement_trie_prefix_tree/Trie.php
new file mode 100644
index 0000000..cee676b
--- /dev/null
+++ b/src/main/php/g0201_0300/s0208_implement_trie_prefix_tree/Trie.php
@@ -0,0 +1,85 @@
+<?php
+
+namespace leetcode\g0201_0300\s0208_implement_trie_prefix_tree;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #String #Hash_Table #Design #Trie
+// #Level_2_Day_16_Design #Udemy_Trie_and_Heap
+// #Big_O_Time_O(word.length())_or_O(prefix.length())_Space_O(N)
+// #2023_12_21_Time_83_ms_(46.67%)_Space_52.1_MB_(6.67%)
+
+class TrieNode {
+    public $children;
+    public $isWord;
+
+    function __construct() {
+        $this->children = array_fill(0, 26, null);
+        $this->isWord = false;
+    }
+}
+
+class Trie {
+    private $root;
+    private $startWith;
+
+    function __construct() {
+        $this->root = new TrieNode();
+        $this->startWith = false;
+    }
+
+    /**
+     * @param String $word
+     * @return NULL
+     */
+    public function insert($word) {
+        $this->insertInternal($word, $this->root, 0);
+    }
+
+    private function insertInternal($word, $root, $idx) {
+        if ($idx == strlen($word)) {
+            $root->isWord = true;
+            return;
+        }
+        $index = ord($word[$idx]) - ord('a');
+        if ($root->children[$index] == null) {
+            $root->children[$index] = new TrieNode();
+        }
+        $this->insertInternal($word, $root->children[$index], $idx + 1);
+    }
+
+    /**
+     * @param String $word
+     * @return Boolean
+     */
+    public function search($word) {
+        return $this->searchInternal($word, $this->root, 0);
+    }
+
+    private function searchInternal($word, $root, $idx) {
+        if ($idx == strlen($word)) {
+            $this->startWith = true;
+            return $root->isWord;
+        }
+        $index = ord($word[$idx]) - ord('a');
+        if ($root->children[$index] == null) {
+            $this->startWith = false;
+            return false;
+        }
+        return $this->searchInternal($word, $root->children[$index], $idx + 1);
+    }
+
+    /**
+     * @param String $prefix
+     * @return Boolean
+     */
+    public function startsWith($prefix) {
+        $this->search($prefix);
+        return $this->startWith;
+    }
+}
+/**
+ * Your Trie object will be instantiated and called as such:
+ * $obj = Trie();
+ * $obj->insert($word);
+ * $ret_2 = $obj->search($word);
+ * $ret_3 = $obj->startsWith($prefix);
+ */
diff --git a/src/main/php/g0201_0300/s0208_implement_trie_prefix_tree/readme.md b/src/main/php/g0201_0300/s0208_implement_trie_prefix_tree/readme.md
new file mode 100644
index 0000000..8121de3
--- /dev/null
+++ b/src/main/php/g0201_0300/s0208_implement_trie_prefix_tree/readme.md
@@ -0,0 +1,36 @@
+208\. Implement Trie (Prefix Tree)
+
+Medium
+
+A [**trie**](https://en.wikipedia.org/wiki/Trie) (pronounced as "try") or **prefix tree** is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker.
+
+Implement the Trie class:
+
+*   `Trie()` Initializes the trie object.
+*   `void insert(String word)` Inserts the string `word` into the trie.
+*   `boolean search(String word)` Returns `true` if the string `word` is in the trie (i.e., was inserted before), and `false` otherwise.
+*   `boolean startsWith(String prefix)` Returns `true` if there is a previously inserted string `word` that has the prefix `prefix`, and `false` otherwise.
+
+**Example 1:**
+
+**Input**
+
+    ["Trie", "insert", "search", "search", "startsWith", "insert", "search"]
+    [[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
+
+**Output:** [null, null, true, false, true, null, true]
+
+**Explanation:**
+
+    Trie trie = new Trie();
+    trie.insert("apple"); trie.search("apple"); // return True
+    trie.search("app"); // return False
+    trie.startsWith("app"); // return True
+    trie.insert("app");
+    trie.search("app"); // return True 
+
+**Constraints:**
+
+*   `1 <= word.length, prefix.length <= 2000`
+*   `word` and `prefix` consist only of lowercase English letters.
+*   At most <code>3 * 10<sup>4</sup></code> calls **in total** will be made to `insert`, `search`, and `startsWith`.
\ No newline at end of file
diff --git a/src/main/php/g0201_0300/s0215_kth_largest_element_in_an_array/Solution.php b/src/main/php/g0201_0300/s0215_kth_largest_element_in_an_array/Solution.php
new file mode 100644
index 0000000..538fe7a
--- /dev/null
+++ b/src/main/php/g0201_0300/s0215_kth_largest_element_in_an_array/Solution.php
@@ -0,0 +1,20 @@
+<?php
+
+namespace leetcode\g0201_0300\s0215_kth_largest_element_in_an_array;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Sorting #Heap_Priority_Queue
+// #Divide_and_Conquer #Quickselect #Data_Structure_II_Day_20_Heap_Priority_Queue
+// #Big_O_Time_O(n*log(n))_Space_O(log(n)) #2023_12_21_Time_222_ms_(49.15%)_Space_29.8_MB_(100.00%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @param Integer $k
+     * @return Integer
+     */
+    function findKthLargest($nums, $k) {
+        $n = count($nums);
+        sort($nums);
+        return $nums[$n - $k];
+    }
+}
diff --git a/src/main/php/g0201_0300/s0215_kth_largest_element_in_an_array/readme.md b/src/main/php/g0201_0300/s0215_kth_largest_element_in_an_array/readme.md
new file mode 100644
index 0000000..c4c64cb
--- /dev/null
+++ b/src/main/php/g0201_0300/s0215_kth_largest_element_in_an_array/readme.md
@@ -0,0 +1,24 @@
+215\. Kth Largest Element in an Array
+
+Medium
+
+Given an integer array `nums` and an integer `k`, return _the_ <code>k<sup>th</sup></code> _largest element in the array_.
+
+Note that it is the <code>k<sup>th</sup></code> largest element in the sorted order, not the <code>k<sup>th</sup></code> distinct element.
+
+**Example 1:**
+
+**Input:** nums = [3,2,1,5,6,4], k = 2
+
+**Output:** 5 
+
+**Example 2:**
+
+**Input:** nums = [3,2,3,1,2,4,5,5,6], k = 4
+
+**Output:** 4 
+
+**Constraints:**
+
+*   <code>1 <= k <= nums.length <= 10<sup>4</sup></code>
+*   <code>-10<sup>4</sup> <= nums[i] <= 10<sup>4</sup></code>
\ No newline at end of file
diff --git a/src/main/php/g0201_0300/s0221_maximal_square/Solution.php b/src/main/php/g0201_0300/s0221_maximal_square/Solution.php
new file mode 100644
index 0000000..42388c1
--- /dev/null
+++ b/src/main/php/g0201_0300/s0221_maximal_square/Solution.php
@@ -0,0 +1,38 @@
+<?php
+
+namespace leetcode\g0201_0300\s0221_maximal_square;
+
+// #Medium #Top_100_Liked_Questions #Array #Dynamic_Programming #Matrix
+// #Dynamic_Programming_I_Day_16 #Big_O_Time_O(m*n)_Space_O(m*n)
+// #2023_12_21_Time_209_ms_(83.33%)_Space_40.6_MB_(100.00%)
+
+class Solution {
+    /**
+     * @param String[][] $matrix
+     * @return Integer
+     */
+    public function maximalSquare($matrix) {
+        $m = count($matrix);
+        if ($m == 0) {
+            return 0;
+        }
+        $n = count($matrix[0]);
+        if ($n == 0) {
+            return 0;
+        }
+        $dp = array_fill(0, $m + 1, array_fill(0, $n + 1, 0));
+        $max = 0;
+        for ($i = 0; $i < $m; $i++) {
+            for ($j = 0; $j < $n; $j++) {
+                if ($matrix[$i][$j] == '1') {
+                    $next = 1 + min($dp[$i][$j], min($dp[$i + 1][$j], $dp[$i][$j + 1]));
+                    if ($next > $max) {
+                        $max = $next;
+                    }
+                    $dp[$i + 1][$j + 1] = $next;
+                }
+            }
+        }
+        return $max * $max;
+    }
+}
diff --git a/src/main/php/g0201_0300/s0221_maximal_square/readme.md b/src/main/php/g0201_0300/s0221_maximal_square/readme.md
new file mode 100644
index 0000000..d9d3909
--- /dev/null
+++ b/src/main/php/g0201_0300/s0221_maximal_square/readme.md
@@ -0,0 +1,34 @@
+221\. Maximal Square
+
+Medium
+
+Given an `m x n` binary `matrix` filled with `0`'s and `1`'s, _find the largest square containing only_ `1`'s _and return its area_.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/11/26/max1grid.jpg)
+
+**Input:** matrix = [["1","0","1","0","0"],["1","0","1","1","1"],["1","1","1","1","1"],["1","0","0","1","0"]]
+
+**Output:** 4 
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2020/11/26/max2grid.jpg)
+
+**Input:** matrix = [["0","1"],["1","0"]]
+
+**Output:** 1 
+
+**Example 3:**
+
+**Input:** matrix = [["0"]]
+
+**Output:** 0 
+
+**Constraints:**
+
+*   `m == matrix.length`
+*   `n == matrix[i].length`
+*   `1 <= m, n <= 300`
+*   `matrix[i][j]` is `'0'` or `'1'`.
\ No newline at end of file
diff --git a/src/main/php/g0201_0300/s0226_invert_binary_tree/Solution.php b/src/main/php/g0201_0300/s0226_invert_binary_tree/Solution.php
new file mode 100644
index 0000000..c1ba745
--- /dev/null
+++ b/src/main/php/g0201_0300/s0226_invert_binary_tree/Solution.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace leetcode\g0201_0300\s0226_invert_binary_tree;
+
+// #Easy #Top_100_Liked_Questions #Depth_First_Search #Breadth_First_Search #Tree #Binary_Tree
+// #Data_Structure_I_Day_12_Tree #Level_2_Day_6_Tree #Udemy_Tree_Stack_Queue
+// #Big_O_Time_O(n)_Space_O(n) #2023_12_21_Time_6_ms_(62.79%)_Space_19.6_MB_(13.18%)
+
+/**
+ * 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 $root
+     * @return TreeNode
+     */
+    public function invertTree($root) {
+        if ($root == null) {
+            return null;
+        }
+        $temp = $root->left;
+        $root->left = $this->invertTree($root->right);
+        $root->right = $this->invertTree($temp);
+        return $root;
+    }
+}
diff --git a/src/main/php/g0201_0300/s0226_invert_binary_tree/readme.md b/src/main/php/g0201_0300/s0226_invert_binary_tree/readme.md
new file mode 100644
index 0000000..339bf4e
--- /dev/null
+++ b/src/main/php/g0201_0300/s0226_invert_binary_tree/readme.md
@@ -0,0 +1,32 @@
+226\. Invert Binary Tree
+
+Easy
+
+Given the `root` of a binary tree, invert the tree, and return _its root_.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2021/03/14/invert1-tree.jpg)
+
+**Input:** root = [4,2,7,1,3,6,9]
+
+**Output:** [4,7,2,9,6,3,1] 
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2021/03/14/invert2-tree.jpg)
+
+**Input:** root = [2,1,3]
+
+**Output:** [2,3,1] 
+
+**Example 3:**
+
+**Input:** root = []
+
+**Output:** [] 
+
+**Constraints:**
+
+*   The number of nodes in the tree is in the range `[0, 100]`.
+*   `-100 <= Node.val <= 100`
\ No newline at end of file
diff --git a/src/test/php/g0101_0200/s0169_majority_element/SolutionTest.php b/src/test/php/g0101_0200/s0169_majority_element/SolutionTest.php
new file mode 100644
index 0000000..96f2037
--- /dev/null
+++ b/src/test/php/g0101_0200/s0169_majority_element/SolutionTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace leetcode\g0101_0200\s0169_majority_element;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testMajorityElement() {
+        $this->assertEquals(3, (new Solution())->majorityElement(array(3, 2, 3)));
+    }
+
+    public function testMajorityElement2() {
+        $this->assertEquals(2, (new Solution())->majorityElement(array(2, 2, 1, 1, 1, 2, 2)));
+    }
+}
diff --git a/src/test/php/g0101_0200/s0189_rotate_array/SolutionTest.php b/src/test/php/g0101_0200/s0189_rotate_array/SolutionTest.php
new file mode 100644
index 0000000..4815a59
--- /dev/null
+++ b/src/test/php/g0101_0200/s0189_rotate_array/SolutionTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace leetcode\g0101_0200\s0189_rotate_array;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testRotate() {
+        $array = array(1, 2, 3, 4, 5, 6, 7);
+        (new Solution())->rotate($array, 3);
+        $this->assertEquals(array(5, 6, 7, 1, 2, 3, 4), $array);
+    }
+
+    public function testRotate2() {
+        $array = array(-1, -100, 3, 99);
+        (new Solution())->rotate($array, 2);
+        $this->assertEquals(array(3, 99, -1, -100), $array);
+    }
+}
diff --git a/src/test/php/g0101_0200/s0198_house_robber/SolutionTest.php b/src/test/php/g0101_0200/s0198_house_robber/SolutionTest.php
new file mode 100644
index 0000000..6332366
--- /dev/null
+++ b/src/test/php/g0101_0200/s0198_house_robber/SolutionTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace leetcode\g0101_0200\s0198_house_robber;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testRob() {
+        $this->assertEquals(4, (new Solution())->rob(array(1, 2, 3, 1)));
+    }
+
+    public function testRob2() {
+        $this->assertEquals(12, (new Solution())->rob(array(2, 7, 9, 3, 1)));
+    }
+}
diff --git a/src/test/php/g0101_0200/s0200_number_of_islands/SolutionTest.php b/src/test/php/g0101_0200/s0200_number_of_islands/SolutionTest.php
new file mode 100644
index 0000000..e913334
--- /dev/null
+++ b/src/test/php/g0101_0200/s0200_number_of_islands/SolutionTest.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace leetcode\g0101_0200\s0200_number_of_islands;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testNumIslands() {
+        $this->assertEquals(1, (new Solution())->numIslands(array(
+            array('1', '1', '1', '1', '0'),
+            array('1', '1', '0', '1', '0'),
+            array('1', '1', '0', '0', '0'),
+            array('0', '0', '0', '0', '0')
+        )));
+    }
+
+    public function testNumIslands2() {
+        $this->assertEquals(3, (new Solution())->numIslands(array(
+            array('1', '1', '0', '0', '0'),
+            array('1', '1', '0', '0', '0'),
+            array('0', '0', '1', '0', '0'),
+            array('0', '0', '0', '1', '1')
+        )));
+    }
+}
diff --git a/src/test/php/g0201_0300/s0206_reverse_linked_list/SolutionTest.php b/src/test/php/g0201_0300/s0206_reverse_linked_list/SolutionTest.php
new file mode 100644
index 0000000..919667c
--- /dev/null
+++ b/src/test/php/g0201_0300/s0206_reverse_linked_list/SolutionTest.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace leetcode\g0201_0300\s0206_reverse_linked_list;
+
+use PHPUnit\Framework\TestCase;
+use leetcode\com_github_leetcode\ListNode;
+
+class SolutionTest extends TestCase {
+    public function testReverseList() {
+        $headActual = new ListNode(1);
+        $headActual->next = new ListNode(2);
+        $headActual->next->next = new ListNode(3);
+        $headActual->next->next->next = new ListNode(4);
+        $headActual->next->next->next->next = new ListNode(5);
+        $this->assertEquals("5, 4, 3, 2, 1", (new Solution())->reverseList($headActual)->toString());
+    }
+
+    public function testReverseList2() {
+        $headActual = new ListNode(1);
+        $headActual->next = new ListNode(2);
+        $this->assertEquals("2, 1", (new Solution())->reverseList($headActual)->toString());
+    }
+
+    public function testReverseList3() {
+        $this->assertEquals(null, (new Solution())->reverseList(null));
+    }
+}
diff --git a/src/test/php/g0201_0300/s0207_course_schedule/SolutionTest.php b/src/test/php/g0201_0300/s0207_course_schedule/SolutionTest.php
new file mode 100644
index 0000000..de65a83
--- /dev/null
+++ b/src/test/php/g0201_0300/s0207_course_schedule/SolutionTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace leetcode\g0201_0300\s0207_course_schedule;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testCanFinish() {
+        $this->assertEquals(true, (new Solution())->canFinish(2, array(array(1, 0))));
+    }
+
+    public function testCanFinish2() {
+        $this->assertEquals(false, (new Solution())->canFinish(2, array(array(1, 0), array(0, 1))));
+    }
+}
diff --git a/src/test/php/g0201_0300/s0208_implement_trie_prefix_tree/TrieTest.php b/src/test/php/g0201_0300/s0208_implement_trie_prefix_tree/TrieTest.php
new file mode 100644
index 0000000..d946203
--- /dev/null
+++ b/src/test/php/g0201_0300/s0208_implement_trie_prefix_tree/TrieTest.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace leetcode\g0201_0300\s0208_implement_trie_prefix_tree;
+
+use PHPUnit\Framework\TestCase;
+
+class TrieTest extends TestCase {
+    public function testTrie() {
+        $trie = new Trie();
+        $trie->insert("apple");
+        $this->assertEquals(true, $trie->search("apple"));
+        $this->assertEquals(false, $trie->search("app"));
+        $this->assertEquals(true, $trie->startsWith("app"));
+        $trie->insert("app");
+        $this->assertEquals(true, $trie->search("app"));
+    }
+}
diff --git a/src/test/php/g0201_0300/s0215_kth_largest_element_in_an_array/SolutionTest.php b/src/test/php/g0201_0300/s0215_kth_largest_element_in_an_array/SolutionTest.php
new file mode 100644
index 0000000..3308f55
--- /dev/null
+++ b/src/test/php/g0201_0300/s0215_kth_largest_element_in_an_array/SolutionTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace leetcode\g0201_0300\s0215_kth_largest_element_in_an_array;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testFindKthLargest() {
+        $this->assertEquals(5, (new Solution())->findKthLargest(array(3, 2, 1, 5, 6, 4), 2));
+    }
+
+    public function testFindKthLargest2() {
+        $this->assertEquals(4, (new Solution())->findKthLargest(array(3, 2, 3, 1, 2, 4, 5, 5, 6), 4));
+    }
+}
diff --git a/src/test/php/g0201_0300/s0221_maximal_square/SolutionTest.php b/src/test/php/g0201_0300/s0221_maximal_square/SolutionTest.php
new file mode 100644
index 0000000..4697e34
--- /dev/null
+++ b/src/test/php/g0201_0300/s0221_maximal_square/SolutionTest.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace leetcode\g0201_0300\s0221_maximal_square;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testMaximalSquare() {
+        $input = array(
+            array('1', '0', '1', '0', '0'),
+            array('1', '0', '1', '1', '1'),
+            array('1', '1', '1', '1', '1'),
+            array('1', '0', '0', '1', '0')
+        );
+        $this->assertEquals(4, (new Solution())->maximalSquare($input));
+    }
+
+    public function testMaximalSquare2() {
+        $input = array(array('0', '1'), array('1', '0'));
+        $this->assertEquals(1, (new Solution())->maximalSquare($input));
+    }
+
+    public function testMaximalSquare3() {
+        $input = array(array('0'));
+        $this->assertEquals(0, (new Solution())->maximalSquare($input));
+    }
+}
diff --git a/src/test/php/g0201_0300/s0226_invert_binary_tree/SolutionTest.php b/src/test/php/g0201_0300/s0226_invert_binary_tree/SolutionTest.php
new file mode 100644
index 0000000..b39f7b2
--- /dev/null
+++ b/src/test/php/g0201_0300/s0226_invert_binary_tree/SolutionTest.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace leetcode\g0201_0300\s0226_invert_binary_tree;
+
+use PHPUnit\Framework\TestCase;
+use leetcode\com_github_leetcode\TreeUtils;
+
+class SolutionTest extends TestCase {
+    public function testInvertTree() {
+        $root = TreeUtils::constructBinaryTree(array(4, 2, 7, 1, 3, 6, 9));
+        $this->assertEquals("4,7,9,6,2,3,1", (new Solution())->invertTree($root));
+    }
+
+    public function testInvertTree2() {
+        $root = TreeUtils::constructBinaryTree(array(2, 1, 3));
+        $this->assertEquals("2,3,1", (new Solution())->invertTree($root));
+    }
+}