From 1d4535a154bba9e68c667dce860491e8a163e2dc Mon Sep 17 00:00:00 2001
From: Valentyn Kolesnikov <javadev75@gmail.com>
Date: Sat, 9 Dec 2023 04:33:44 +0200
Subject: [PATCH] Added tasks 31-46

---
 .../php/g0001_0100/s0001_two_sum/Solution.php |  2 +-
 .../s0002_add_two_numbers/Solution.php        |  2 +-
 .../Solution.php                              |  2 +-
 .../Solution.php                              |  2 +-
 .../s0006_zigzag_conversion/Solution.php      |  2 +-
 .../s0007_reverse_integer/Solution.php        |  6 ++-
 .../s0008_string_to_integer_atoi/Solution.php |  2 +-
 .../s0009_palindrome_number/Solution.php      |  2 +-
 .../Solution.php                              |  5 ++
 .../s0022_generate_parentheses/Solution.php   |  4 +-
 .../s0023_merge_k_sorted_lists/Solution.php   |  2 +-
 .../s0024_swap_nodes_in_pairs/Solution.php    |  2 +-
 .../Solution.php                              |  2 +-
 .../s0031_next_permutation/Solution.php       | 42 +++++++++++++++
 .../s0031_next_permutation/readme.md          | 38 ++++++++++++++
 .../Solution.php                              | 52 +++++++++++++++++++
 .../s0032_longest_valid_parentheses/readme.md | 32 ++++++++++++
 .../Solution.php                              | 38 ++++++++++++++
 .../readme.md                                 | 37 +++++++++++++
 .../Solution.php                              | 39 ++++++++++++++
 .../readme.md                                 | 34 ++++++++++++
 .../s0035_search_insert_position/Solution.php | 30 +++++++++++
 .../s0035_search_insert_position/readme.md    | 44 ++++++++++++++++
 .../s0039_combination_sum/Solution.php        | 37 +++++++++++++
 .../s0039_combination_sum/readme.md           | 52 +++++++++++++++++++
 .../s0041_first_missing_positive/Solution.php | 24 +++++++++
 .../s0041_first_missing_positive/readme.md    | 30 +++++++++++
 .../s0042_trapping_rain_water/Solution.php    | 33 ++++++++++++
 .../s0042_trapping_rain_water/readme.md       | 27 ++++++++++
 .../s0045_jump_game_ii/Solution.php           | 32 ++++++++++++
 .../g0001_0100/s0045_jump_game_ii/readme.md   | 30 +++++++++++
 .../s0046_permutations/Solution.php           | 40 ++++++++++++++
 .../g0001_0100/s0046_permutations/readme.md   | 29 +++++++++++
 .../s0031_next_permutation/SolutionTest.php   | 25 +++++++++
 .../SolutionTest.php                          | 19 +++++++
 .../SolutionTest.php                          | 19 +++++++
 .../SolutionTest.php                          | 25 +++++++++
 .../SolutionTest.php                          | 19 +++++++
 .../s0039_combination_sum/SolutionTest.php    | 28 ++++++++++
 .../SolutionTest.php                          | 19 +++++++
 .../SolutionTest.php                          | 15 ++++++
 .../s0045_jump_game_ii/SolutionTest.php       | 15 ++++++
 .../s0046_permutations/SolutionTest.php       | 23 ++++++++
 43 files changed, 949 insertions(+), 13 deletions(-)
 create mode 100644 src/main/php/g0001_0100/s0031_next_permutation/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0031_next_permutation/readme.md
 create mode 100644 src/main/php/g0001_0100/s0032_longest_valid_parentheses/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0032_longest_valid_parentheses/readme.md
 create mode 100644 src/main/php/g0001_0100/s0033_search_in_rotated_sorted_array/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0033_search_in_rotated_sorted_array/readme.md
 create mode 100644 src/main/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/readme.md
 create mode 100644 src/main/php/g0001_0100/s0035_search_insert_position/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0035_search_insert_position/readme.md
 create mode 100644 src/main/php/g0001_0100/s0039_combination_sum/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0039_combination_sum/readme.md
 create mode 100644 src/main/php/g0001_0100/s0041_first_missing_positive/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0041_first_missing_positive/readme.md
 create mode 100644 src/main/php/g0001_0100/s0042_trapping_rain_water/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0042_trapping_rain_water/readme.md
 create mode 100644 src/main/php/g0001_0100/s0045_jump_game_ii/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0045_jump_game_ii/readme.md
 create mode 100644 src/main/php/g0001_0100/s0046_permutations/Solution.php
 create mode 100644 src/main/php/g0001_0100/s0046_permutations/readme.md
 create mode 100644 src/test/php/g0001_0100/s0031_next_permutation/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0032_longest_valid_parentheses/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0033_search_in_rotated_sorted_array/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0035_search_insert_position/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0039_combination_sum/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0041_first_missing_positive/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0042_trapping_rain_water/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0045_jump_game_ii/SolutionTest.php
 create mode 100644 src/test/php/g0001_0100/s0046_permutations/SolutionTest.php

diff --git a/src/main/php/g0001_0100/s0001_two_sum/Solution.php b/src/main/php/g0001_0100/s0001_two_sum/Solution.php
index dd0c725..00a19f3 100644
--- a/src/main/php/g0001_0100/s0001_two_sum/Solution.php
+++ b/src/main/php/g0001_0100/s0001_two_sum/Solution.php
@@ -12,7 +12,7 @@ class Solution {
      * @param Integer $target
      * @return Integer[]
      */
-    function twoSum($nums, $target) {
+    public function twoSum($nums, $target) {
         $ind = [];
         for ($i = 0; $i < count($nums); ++$i) {
             $complement = $target - $nums[$i];
diff --git a/src/main/php/g0001_0100/s0002_add_two_numbers/Solution.php b/src/main/php/g0001_0100/s0002_add_two_numbers/Solution.php
index 604c609..8b41bbb 100644
--- a/src/main/php/g0001_0100/s0002_add_two_numbers/Solution.php
+++ b/src/main/php/g0001_0100/s0002_add_two_numbers/Solution.php
@@ -25,7 +25,7 @@ class Solution {
      * @param ListNode $l2
      * @return ListNode
      */
-    function addTwoNumbers($l1, $l2) {
+    public function addTwoNumbers($l1, $l2) {
         $dummyHead = new ListNode(0);
         $p = $l1;
         $q = $l2;
diff --git a/src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/Solution.php b/src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/Solution.php
index ca60cbc..a625ebb 100644
--- a/src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/Solution.php
+++ b/src/main/php/g0001_0100/s0004_median_of_two_sorted_arrays/Solution.php
@@ -11,7 +11,7 @@ class Solution {
      * @param Integer[] $nums2
      * @return Float
      */
-    function findMedianSortedArrays($nums1, $nums2) {
+    public function findMedianSortedArrays($nums1, $nums2) {
         $nums3 = [];
         $sum = count($nums1) + count($nums2);
         $med = ($sum / 2);
diff --git a/src/main/php/g0001_0100/s0005_longest_palindromic_substring/Solution.php b/src/main/php/g0001_0100/s0005_longest_palindromic_substring/Solution.php
index 870b3b9..e036a2e 100644
--- a/src/main/php/g0001_0100/s0005_longest_palindromic_substring/Solution.php
+++ b/src/main/php/g0001_0100/s0005_longest_palindromic_substring/Solution.php
@@ -12,7 +12,7 @@ class Solution {
      * @param String $s
      * @return String
      */
-    function longestPalindrome($s): string {
+    public function longestPalindrome($s): string {
         if (($length = strlen($s)) <= 1) {
             return $s;
         }
diff --git a/src/main/php/g0001_0100/s0006_zigzag_conversion/Solution.php b/src/main/php/g0001_0100/s0006_zigzag_conversion/Solution.php
index 754f890..d9cdbe7 100644
--- a/src/main/php/g0001_0100/s0006_zigzag_conversion/Solution.php
+++ b/src/main/php/g0001_0100/s0006_zigzag_conversion/Solution.php
@@ -10,7 +10,7 @@ class Solution {
      * @param Integer $numRows
      * @return String
      */
-    function convert($s, $numRows) {
+    public function convert($s, $numRows) {
         if ($numRows == 1) {
             return $s;
         }
diff --git a/src/main/php/g0001_0100/s0007_reverse_integer/Solution.php b/src/main/php/g0001_0100/s0007_reverse_integer/Solution.php
index b98420e..bbe3455 100644
--- a/src/main/php/g0001_0100/s0007_reverse_integer/Solution.php
+++ b/src/main/php/g0001_0100/s0007_reverse_integer/Solution.php
@@ -6,7 +6,11 @@
 // #2023_12_03_Time_3_ms_(90.99%)_Space_19.2_MB_(44.23%)
 
 class Solution {
-    function reverse($x) {
+    /**
+     * @param Integer $x
+     * @return Integer
+     */
+    public function reverse($x) {
         $ls_negative = '';
         if (strpos($x, '-') === 0) {
             $ls_negative = substr($x, 0, 1);
diff --git a/src/main/php/g0001_0100/s0008_string_to_integer_atoi/Solution.php b/src/main/php/g0001_0100/s0008_string_to_integer_atoi/Solution.php
index 9804c2b..7212b5e 100644
--- a/src/main/php/g0001_0100/s0008_string_to_integer_atoi/Solution.php
+++ b/src/main/php/g0001_0100/s0008_string_to_integer_atoi/Solution.php
@@ -9,7 +9,7 @@ class Solution {
      * @param String $s
      * @return Integer
      */
-    function myAtoi($s) {
+    public function myAtoi($s) {
         $pos = 0;
         $res = 0;
         for ($i = 0; $i < strlen($s); $i++) {
diff --git a/src/main/php/g0001_0100/s0009_palindrome_number/Solution.php b/src/main/php/g0001_0100/s0009_palindrome_number/Solution.php
index bf49357..bbd6dae 100644
--- a/src/main/php/g0001_0100/s0009_palindrome_number/Solution.php
+++ b/src/main/php/g0001_0100/s0009_palindrome_number/Solution.php
@@ -9,7 +9,7 @@ class Solution {
      * @param Integer $x
      * @return Boolean
      */
-    function isPalindrome($x) {
+    public function isPalindrome($x) {
         if ($x < 0) {
             return false;
         }
diff --git a/src/main/php/g0001_0100/s0019_remove_nth_node_from_end_of_list/Solution.php b/src/main/php/g0001_0100/s0019_remove_nth_node_from_end_of_list/Solution.php
index 7b22699..9dc1806 100644
--- a/src/main/php/g0001_0100/s0019_remove_nth_node_from_end_of_list/Solution.php
+++ b/src/main/php/g0001_0100/s0019_remove_nth_node_from_end_of_list/Solution.php
@@ -23,6 +23,11 @@
 class Solution {
     private $n;
 
+    /**
+     * @param ListNode $head
+     * @param Integer $n
+     * @return ListNode
+     */
     public function removeNthFromEnd($head, $n) {
         $this->n = $n;
         $node = new ListNode(0, $head);
diff --git a/src/main/php/g0001_0100/s0022_generate_parentheses/Solution.php b/src/main/php/g0001_0100/s0022_generate_parentheses/Solution.php
index 938616d..f8fe3a6 100644
--- a/src/main/php/g0001_0100/s0022_generate_parentheses/Solution.php
+++ b/src/main/php/g0001_0100/s0022_generate_parentheses/Solution.php
@@ -11,13 +11,13 @@ class Solution {
      * @param Integer $n
      * @return String[]
      */
-    function generateParenthesis(int $n): array {
+    public function generateParenthesis(int $n): array {
         $sb = '';
         $ans = [];
         return $this->generate($sb, $ans, $n, $n);
     }
 
-    function generate(string &$sb, array &$ans, int $open, int $close): array {
+    private function generate(string &$sb, array &$ans, int $open, int $close): array {
         if ($open === 0 && $close === 0) {
             $ans[] = $sb;
             return $ans;
diff --git a/src/main/php/g0001_0100/s0023_merge_k_sorted_lists/Solution.php b/src/main/php/g0001_0100/s0023_merge_k_sorted_lists/Solution.php
index 5ec4930..092d4db 100644
--- a/src/main/php/g0001_0100/s0023_merge_k_sorted_lists/Solution.php
+++ b/src/main/php/g0001_0100/s0023_merge_k_sorted_lists/Solution.php
@@ -24,7 +24,7 @@ class Solution {
      * @param ListNode[] $lists
      * @return ListNode
      */
-    function mergeKLists($lists) {
+    public function mergeKLists($lists) {
         $heap = new \SplMinHeap();
         $head = [];
         foreach ($lists as $list) {
diff --git a/src/main/php/g0001_0100/s0024_swap_nodes_in_pairs/Solution.php b/src/main/php/g0001_0100/s0024_swap_nodes_in_pairs/Solution.php
index 9ddc704..82e3068 100644
--- a/src/main/php/g0001_0100/s0024_swap_nodes_in_pairs/Solution.php
+++ b/src/main/php/g0001_0100/s0024_swap_nodes_in_pairs/Solution.php
@@ -24,7 +24,7 @@ class Solution {
      * @param ListNode $head
      * @return ListNode
      */
-    function swapPairs($head) {
+    public function swapPairs($head) {
         $output = new ListNode(0);
         $output->next = $head;
         $point = $output;
diff --git a/src/main/php/g0001_0100/s0025_reverse_nodes_in_k_group/Solution.php b/src/main/php/g0001_0100/s0025_reverse_nodes_in_k_group/Solution.php
index e9f5728..8b385c5 100644
--- a/src/main/php/g0001_0100/s0025_reverse_nodes_in_k_group/Solution.php
+++ b/src/main/php/g0001_0100/s0025_reverse_nodes_in_k_group/Solution.php
@@ -25,7 +25,7 @@ class Solution {
      * @param Integer $k
      * @return ListNode
      */
-    function reverseKGroup($head, $k) {
+    public function reverseKGroup($head, $k) {
         if ($this->countNodesInList($head) < $k || $head->next == null || $head == null) {
             return $head;
         } else {
diff --git a/src/main/php/g0001_0100/s0031_next_permutation/Solution.php b/src/main/php/g0001_0100/s0031_next_permutation/Solution.php
new file mode 100644
index 0000000..7e00c49
--- /dev/null
+++ b/src/main/php/g0001_0100/s0031_next_permutation/Solution.php
@@ -0,0 +1,42 @@
+<?php
+
+namespace leetcode\g0001_0100\s0031_next_permutation;
+
+// #Medium #Top_100_Liked_Questions #Array #Two_Pointers #Big_O_Time_O(n)_Space_O(1)
+// #2023_12_09_Time_7_ms_(86.36%)_Space_18.6_MB_(100.00%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return NULL
+     */
+    public function nextPermutation(&$nums) {
+        if ($nums == null || count($nums) <= 1) {
+            return;
+        }
+        $i = count($nums) - 2;
+        while ($i >= 0 && $nums[$i] >= $nums[$i + 1]) {
+            $i--;
+        }
+        if ($i >= 0) {
+            $j = count($nums) - 1;
+            while ($nums[$j] <= $nums[$i]) {
+                $j--;
+            }
+            $this->swap($nums, $i, $j);
+        }
+        $this->reverse($nums, $i + 1, count($nums) - 1);
+    }
+
+    private function swap(&$nums, $i, $j) {
+        $temp = $nums[$i];
+        $nums[$i] = $nums[$j];
+        $nums[$j] = $temp;
+    }
+
+    private function reverse(&$nums, $i, $j) {
+        while ($i < $j) {
+            $this->swap($nums, $i++, $j--);
+        }
+    }
+}
diff --git a/src/main/php/g0001_0100/s0031_next_permutation/readme.md b/src/main/php/g0001_0100/s0031_next_permutation/readme.md
new file mode 100644
index 0000000..bf3ed98
--- /dev/null
+++ b/src/main/php/g0001_0100/s0031_next_permutation/readme.md
@@ -0,0 +1,38 @@
+31\. Next Permutation
+
+Medium
+
+Implement **next permutation**, which rearranges numbers into the lexicographically next greater permutation of numbers.
+
+If such an arrangement is not possible, it must rearrange it as the lowest possible order (i.e., sorted in ascending order).
+
+The replacement must be **[in place](http://en.wikipedia.org/wiki/In-place_algorithm)** and use only constant extra memory.
+
+**Example 1:**
+
+**Input:** nums = [1,2,3]
+
+**Output:** [1,3,2] 
+
+**Example 2:**
+
+**Input:** nums = [3,2,1]
+
+**Output:** [1,2,3] 
+
+**Example 3:**
+
+**Input:** nums = [1,1,5]
+
+**Output:** [1,5,1] 
+
+**Example 4:**
+
+**Input:** nums = [1]
+
+**Output:** [1] 
+
+**Constraints:**
+
+*   `1 <= nums.length <= 100`
+*   `0 <= nums[i] <= 100`
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0032_longest_valid_parentheses/Solution.php b/src/main/php/g0001_0100/s0032_longest_valid_parentheses/Solution.php
new file mode 100644
index 0000000..2a04be6
--- /dev/null
+++ b/src/main/php/g0001_0100/s0032_longest_valid_parentheses/Solution.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace leetcode\g0001_0100\s0032_longest_valid_parentheses;
+
+// #Hard #Top_100_Liked_Questions #String #Dynamic_Programming #Stack #Big_O_Time_O(n)_Space_O(1)
+// #2023_12_09_Time_8_ms_(67.65%)_Space_19.2_MB_(85.29%)
+
+class Solution {
+    /**
+     * @param String $s
+     * @return Integer
+     */
+    public function longestValidParentheses($s) {
+        $max = 0;
+        $left = 0;
+        $right = 0;
+        $n = strlen($s);
+        for ($i = 0; $i < $n; $i++) {
+            $ch = $s[$i];
+            if ($ch == '(') {
+                $left++;
+            } else {
+                $right++;
+            }
+            if ($right > $left) {
+                $left = 0;
+                $right = 0;
+            }
+            if ($left == $right) {
+                $max = max($max, $left + $right);
+            }
+        }
+        $left = 0;
+        $right = 0;
+        for ($i = $n - 1; $i >= 0; $i--) {
+            $ch = $s[$i];
+            if ($ch == '(') {
+                $left++;
+            } else {
+                $right++;
+            }
+            if ($left > $right) {
+                $left = 0;
+                $right = 0;
+            }
+            if ($left == $right) {
+                $max = max($max, $left + $right);
+            }
+        }
+        return $max;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0032_longest_valid_parentheses/readme.md b/src/main/php/g0001_0100/s0032_longest_valid_parentheses/readme.md
new file mode 100644
index 0000000..f11141d
--- /dev/null
+++ b/src/main/php/g0001_0100/s0032_longest_valid_parentheses/readme.md
@@ -0,0 +1,32 @@
+32\. Longest Valid Parentheses
+
+Hard
+
+Given a string containing just the characters `'('` and `')'`, find the length of the longest valid (well-formed) parentheses substring.
+
+**Example 1:**
+
+**Input:** s = "(()"
+
+**Output:** 2
+
+**Explanation:** The longest valid parentheses substring is "()". 
+
+**Example 2:**
+
+**Input:** s = ")()())"
+
+**Output:** 4
+
+**Explanation:** The longest valid parentheses substring is "()()". 
+
+**Example 3:**
+
+**Input:** s = ""
+
+**Output:** 0 
+
+**Constraints:**
+
+*   <code>0 <= s.length <= 3 * 10<sup>4</sup></code>
+*   `s[i]` is `'('`, or `')'`.
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0033_search_in_rotated_sorted_array/Solution.php b/src/main/php/g0001_0100/s0033_search_in_rotated_sorted_array/Solution.php
new file mode 100644
index 0000000..7d2aad5
--- /dev/null
+++ b/src/main/php/g0001_0100/s0033_search_in_rotated_sorted_array/Solution.php
@@ -0,0 +1,38 @@
+<?php
+
+namespace leetcode\g0001_0100\s0033_search_in_rotated_sorted_array;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Binary_Search
+// #Algorithm_II_Day_1_Binary_Search #Binary_Search_I_Day_11 #Level_2_Day_8_Binary_Search
+// #Udemy_Binary_Search #Big_O_Time_O(log_n)_Space_O(1)
+// #2023_12_09_Time_7_ms_(83.17%)_Space_19.1_MB_(83.17%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @param Integer $target
+     * @return Integer
+     */
+    public function search($nums, $target) {
+        $lo = 0;
+        $hi = count($nums) - 1;
+        while ($lo <= $hi) {
+            $mid = (($hi - $lo) >> 1) + $lo;
+            if ($target == $nums[$mid]) {
+                return $mid;
+            }
+            if ($nums[$lo] <= $nums[$mid]) {
+                if ($nums[$lo] <= $target && $target <= $nums[$mid]) {
+                    $hi = $mid - 1;
+                } else {
+                    $lo = $mid + 1;
+                }
+            } elseif ($nums[$mid] <= $target && $target <= $nums[$hi]) {
+                $lo = $mid + 1;
+            } else {
+                $hi = $mid - 1;
+            }
+        }
+        return -1;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0033_search_in_rotated_sorted_array/readme.md b/src/main/php/g0001_0100/s0033_search_in_rotated_sorted_array/readme.md
new file mode 100644
index 0000000..ebfff91
--- /dev/null
+++ b/src/main/php/g0001_0100/s0033_search_in_rotated_sorted_array/readme.md
@@ -0,0 +1,37 @@
+33\. Search in Rotated Sorted Array
+
+Medium
+
+There is an integer array `nums` sorted in ascending order (with **distinct** values).
+
+Prior to being passed to your function, `nums` is **possibly rotated** at an unknown pivot index `k` (`1 <= k < nums.length`) such that the resulting array is `[nums[k], nums[k+1], ..., nums[n-1], nums[0], nums[1], ..., nums[k-1]]` (**0-indexed**). For example, `[0,1,2,4,5,6,7]` might be rotated at pivot index `3` and become `[4,5,6,7,0,1,2]`.
+
+Given the array `nums` **after** the possible rotation and an integer `target`, return _the index of_ `target` _if it is in_ `nums`_, or_ `-1` _if it is not in_ `nums`.
+
+You must write an algorithm with `O(log n)` runtime complexity.
+
+**Example 1:**
+
+**Input:** nums = [4,5,6,7,0,1,2], target = 0
+
+**Output:** 4 
+
+**Example 2:**
+
+**Input:** nums = [4,5,6,7,0,1,2], target = 3
+
+**Output:** -1 
+
+**Example 3:**
+
+**Input:** nums = [1], target = 0
+
+**Output:** -1 
+
+**Constraints:**
+
+*   `1 <= nums.length <= 5000`
+*   <code>-10<sup>4</sup> <= nums[i] <= 10<sup>4</sup></code>
+*   All values of `nums` are **unique**.
+*   `nums` is an ascending array that is possibly rotated.
+*   <code>-10<sup>4</sup> <= target <= 10<sup>4</sup></code>
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/Solution.php b/src/main/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/Solution.php
new file mode 100644
index 0000000..69b8381
--- /dev/null
+++ b/src/main/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/Solution.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace leetcode\g0001_0100\s0034_find_first_and_last_position_of_element_in_sorted_array;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Binary_Search
+// #Algorithm_II_Day_1_Binary_Search #Binary_Search_I_Day_5 #Big_O_Time_O(log_n)_Space_O(1)
+// #2023_12_09_Time_19_ms_(81.01%)_Space_23.5_MB_(22.78%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @param Integer $target
+     * @return Integer[]
+     */
+    public function searchRange($nums, $target) {
+        $ans = array();
+        $ans[0] = $this->helper($nums, $target, false);
+        $ans[1] = $this->helper($nums, $target, true);
+        return $ans;
+    }
+
+    private function helper($nums, $target, $equals) {
+        $l = 0;
+        $r = count($nums) - 1;
+        $result = -1;
+        while ($l <= $r) {
+            $mid = $l + intval(($r - $l) / 2);
+            if ($nums[$mid] == $target) {
+                $result = $mid;
+            }
+            if ($nums[$mid] < $target || ($nums[$mid] == $target && $equals)) {
+                $l = $mid + 1;
+            } else {
+                $r = $mid - 1;
+            }
+        }
+        return $result;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/readme.md b/src/main/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/readme.md
new file mode 100644
index 0000000..7c04eb2
--- /dev/null
+++ b/src/main/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/readme.md
@@ -0,0 +1,34 @@
+34\. Find First and Last Position of Element in Sorted Array
+
+Medium
+
+Given an array of integers `nums` sorted in non-decreasing order, find the starting and ending position of a given `target` value.
+
+If `target` is not found in the array, return `[-1, -1]`.
+
+You must write an algorithm with `O(log n)` runtime complexity.
+
+**Example 1:**
+
+**Input:** nums = [5,7,7,8,8,10], target = 8
+
+**Output:** [3,4] 
+
+**Example 2:**
+
+**Input:** nums = [5,7,7,8,8,10], target = 6
+
+**Output:** [-1,-1] 
+
+**Example 3:**
+
+**Input:** nums = [], target = 0
+
+**Output:** [-1,-1] 
+
+**Constraints:**
+
+*   <code>0 <= nums.length <= 10<sup>5</sup></code>
+*   <code>-10<sup>9</sup> <= nums[i] <= 10<sup>9</sup></code>
+*   `nums` is a non-decreasing array.
+*   <code>-10<sup>9</sup> <= target <= 10<sup>9</sup></code>
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0035_search_insert_position/Solution.php b/src/main/php/g0001_0100/s0035_search_insert_position/Solution.php
new file mode 100644
index 0000000..8c2ac5a
--- /dev/null
+++ b/src/main/php/g0001_0100/s0035_search_insert_position/Solution.php
@@ -0,0 +1,30 @@
+<?php
+
+namespace leetcode\g0001_0100\s0035_search_insert_position;
+
+// #Easy #Top_100_Liked_Questions #Array #Binary_Search #Algorithm_I_Day_1_Binary_Search
+// #Binary_Search_I_Day_2 #Big_O_Time_O(log_n)_Space_O(1)
+// #2023_12_09_Time_8_ms_(85.09%)_Space_19.7_MB_(64.77%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @param Integer $target
+     * @return Integer
+     */
+    public function searchInsert($nums, $target) {
+        $lo = 0;
+        $hi = count($nums) - 1;
+        while ($lo <= $hi) {
+            $mid = $lo + intval(($hi - $lo) / 2);
+            if ($target == $nums[$mid]) {
+                return $mid;
+            } elseif ($target < $nums[$mid]) {
+                $hi = $mid - 1;
+            } elseif ($target > $nums[$mid]) {
+                $lo = $mid + 1;
+            }
+        }
+        return $lo;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0035_search_insert_position/readme.md b/src/main/php/g0001_0100/s0035_search_insert_position/readme.md
new file mode 100644
index 0000000..94ead0d
--- /dev/null
+++ b/src/main/php/g0001_0100/s0035_search_insert_position/readme.md
@@ -0,0 +1,44 @@
+35\. Search Insert Position
+
+Easy
+
+Given a sorted array of distinct integers and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.
+
+You must write an algorithm with `O(log n)` runtime complexity.
+
+**Example 1:**
+
+**Input:** nums = [1,3,5,6], target = 5
+
+**Output:** 2 
+
+**Example 2:**
+
+**Input:** nums = [1,3,5,6], target = 2
+
+**Output:** 1 
+
+**Example 3:**
+
+**Input:** nums = [1,3,5,6], target = 7
+
+**Output:** 4 
+
+**Example 4:**
+
+**Input:** nums = [1,3,5,6], target = 0
+
+**Output:** 0 
+
+**Example 5:**
+
+**Input:** nums = [1], target = 0
+
+**Output:** 0 
+
+**Constraints:**
+
+*   <code>1 <= nums.length <= 10<sup>4</sup></code>
+*   <code>-10<sup>4</sup> <= nums[i] <= 10<sup>4</sup></code>
+*   `nums` contains **distinct** values sorted in **ascending** order.
+*   <code>-10<sup>4</sup> <= target <= 10<sup>4</sup></code>
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0039_combination_sum/Solution.php b/src/main/php/g0001_0100/s0039_combination_sum/Solution.php
new file mode 100644
index 0000000..55f658d
--- /dev/null
+++ b/src/main/php/g0001_0100/s0039_combination_sum/Solution.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace leetcode\g0001_0100\s0039_combination_sum;
+
+// #Medium #Top_100_Liked_Questions #Array #Backtracking #Algorithm_II_Day_10_Recursion_Backtracking
+// #Level_2_Day_20_Brute_Force/Backtracking #Udemy_Backtracking/Recursion
+// #Big_O_Time_O(2^n)_Space_O(n+2^n) #2023_12_09_Time_11_ms_(87.10%)_Space_19.5_MB_(19.36%)
+
+class Solution {
+    /**
+     * @param Integer[] $candidates
+     * @param Integer $target
+     * @return Integer[][]
+     */
+    public function combinationSum($coins, $amount) {
+        $ans = array();
+        $subList = array();
+        $this->combinationSumRec(count($coins), $coins, $amount, $subList, $ans);
+        return $ans;
+    }
+
+    private function combinationSumRec($n, $coins, $amount, &$subList, &$ans) {
+        if ($amount == 0 || $n == 0) {
+            if ($amount == 0) {
+                $base = $subList;
+                array_push($ans, $base);
+            }
+            return;
+        }
+        if ($amount - $coins[$n - 1] >= 0) {
+            array_push($subList, $coins[$n - 1]);
+            $this->combinationSumRec($n, $coins, $amount - $coins[$n - 1], $subList, $ans);
+            array_pop($subList);
+        }
+        $this->combinationSumRec($n - 1, $coins, $amount, $subList, $ans);
+    }
+}
diff --git a/src/main/php/g0001_0100/s0039_combination_sum/readme.md b/src/main/php/g0001_0100/s0039_combination_sum/readme.md
new file mode 100644
index 0000000..1f2c636
--- /dev/null
+++ b/src/main/php/g0001_0100/s0039_combination_sum/readme.md
@@ -0,0 +1,52 @@
+39\. Combination Sum
+
+Medium
+
+Given an array of **distinct** integers `candidates` and a target integer `target`, return _a list of all **unique combinations** of_ `candidates` _where the chosen numbers sum to_ `target`_._ You may return the combinations in **any order**.
+
+The **same** number may be chosen from `candidates` an **unlimited number of times**. Two combinations are unique if the frequency of at least one of the chosen numbers is different.
+
+It is **guaranteed** that the number of unique combinations that sum up to `target` is less than `150` combinations for the given input.
+
+**Example 1:**
+
+**Input:** candidates = [2,3,6,7], target = 7
+
+**Output:** [[2,2,3],[7]]
+
+**Explanation:**
+
+    2 and 3 are candidates, and 2 + 2 + 3 = 7. Note that 2 can be used multiple times.
+    7 is a candidate, and 7 = 7.
+    These are the only two combinations. 
+
+**Example 2:**
+
+**Input:** candidates = [2,3,5], target = 8
+
+**Output:** [[2,2,2,2],[2,3,3],[3,5]] 
+
+**Example 3:**
+
+**Input:** candidates = [2], target = 1
+
+**Output:** [] 
+
+**Example 4:**
+
+**Input:** candidates = [1], target = 1
+
+**Output:** [[1]] 
+
+**Example 5:**
+
+**Input:** candidates = [1], target = 2
+
+**Output:** [[1,1]] 
+
+**Constraints:**
+
+*   `1 <= candidates.length <= 30`
+*   `1 <= candidates[i] <= 200`
+*   All elements of `candidates` are **distinct**.
+*   `1 <= target <= 500`
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0041_first_missing_positive/Solution.php b/src/main/php/g0001_0100/s0041_first_missing_positive/Solution.php
new file mode 100644
index 0000000..6d1597d
--- /dev/null
+++ b/src/main/php/g0001_0100/s0041_first_missing_positive/Solution.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace leetcode\g0001_0100\s0041_first_missing_positive;
+
+// #Hard #Top_100_Liked_Questions #Top_Interview_Questions #Array #Hash_Table #Udemy_Arrays
+// #Big_O_Time_O(n)_Space_O(n) #2023_12_09_Time_111_ms_(90.48%)_Space_33.6_MB_(69.05%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer
+     */
+    public function firstMissingPositive($nums) {
+        $positiveNumbers = array_filter($nums, function ($num) {
+            return $num > 0;
+        });
+        $positiveNumbers = array_flip($positiveNumbers);
+        for ($i = 1; $i <= count($positiveNumbers) + 1; $i++) {
+            if (isset($positiveNumbers[$i]) === false) {
+                return $i;
+            }
+        }
+    }
+}
diff --git a/src/main/php/g0001_0100/s0041_first_missing_positive/readme.md b/src/main/php/g0001_0100/s0041_first_missing_positive/readme.md
new file mode 100644
index 0000000..4cd0b1d
--- /dev/null
+++ b/src/main/php/g0001_0100/s0041_first_missing_positive/readme.md
@@ -0,0 +1,30 @@
+41\. First Missing Positive
+
+Hard
+
+Given an unsorted integer array `nums`, return the smallest missing positive integer.
+
+You must implement an algorithm that runs in `O(n)` time and uses constant extra space.
+
+**Example 1:**
+
+**Input:** nums = [1,2,0]
+
+**Output:** 3 
+
+**Example 2:**
+
+**Input:** nums = [3,4,-1,1]
+
+**Output:** 2 
+
+**Example 3:**
+
+**Input:** nums = [7,8,9,11,12]
+
+**Output:** 1 
+
+**Constraints:**
+
+*   <code>1 <= nums.length <= 5 * 10<sup>5</sup></code>
+*   <code>-2<sup>31</sup> <= nums[i] <= 2<sup>31</sup> - 1</code>
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0042_trapping_rain_water/Solution.php b/src/main/php/g0001_0100/s0042_trapping_rain_water/Solution.php
new file mode 100644
index 0000000..e8879c9
--- /dev/null
+++ b/src/main/php/g0001_0100/s0042_trapping_rain_water/Solution.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace leetcode\g0001_0100\s0042_trapping_rain_water;
+
+// #Hard #Top_100_Liked_Questions #Top_Interview_Questions #Array #Dynamic_Programming #Two_Pointers
+// #Stack #Monotonic_Stack #Dynamic_Programming_I_Day_9 #Udemy_Two_Pointers
+// #Big_O_Time_O(n)_Space_O(1) #2023_12_09_Time_29_ms_(69.15%)_Space_21.5_MB_(97.87%)
+
+class Solution {
+    /**
+     * @param Integer[] $height
+     * @return Integer
+     */
+    public function trap($height) {
+        $result = 0;
+        $i = 0;
+        $j = count($height) - 1;
+        $maxLeft = 0;
+        $maxRight = 0;
+        while ($i < $j) {
+            if ($height[$i] < $height[$j]) {
+                $maxLeft = max($maxLeft, $height[$i]);
+                $result += $maxLeft - $height[$i];
+                $i++;
+            } else {
+                $maxRight = max($maxRight, $height[$j]);
+                $result += $maxRight - $height[$j];
+                $j--;
+            }
+        }
+        return $result;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0042_trapping_rain_water/readme.md b/src/main/php/g0001_0100/s0042_trapping_rain_water/readme.md
new file mode 100644
index 0000000..b57de86
--- /dev/null
+++ b/src/main/php/g0001_0100/s0042_trapping_rain_water/readme.md
@@ -0,0 +1,27 @@
+42\. Trapping Rain Water
+
+Hard
+
+Given `n` non-negative integers representing an elevation map where the width of each bar is `1`, compute how much water it can trap after raining.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2018/10/22/rainwatertrap.png)
+
+**Input:** height = [0,1,0,2,1,0,1,3,2,1,2,1]
+
+**Output:** 6
+
+**Explanation:** The above elevation map (black section) is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped. 
+
+**Example 2:**
+
+**Input:** height = [4,2,0,3,2,5]
+
+**Output:** 9 
+
+**Constraints:**
+
+*   `n == height.length`
+*   <code>1 <= n <= 2 * 10<sup>4</sup></code>
+*   <code>0 <= height[i] <= 10<sup>5</sup></code>
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0045_jump_game_ii/Solution.php b/src/main/php/g0001_0100/s0045_jump_game_ii/Solution.php
new file mode 100644
index 0000000..25a01df
--- /dev/null
+++ b/src/main/php/g0001_0100/s0045_jump_game_ii/Solution.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace leetcode\g0001_0100\s0045_jump_game_ii;
+
+// #Medium #Top_100_Liked_Questions #Array #Dynamic_Programming #Greedy
+// #Algorithm_II_Day_13_Dynamic_Programming #Dynamic_Programming_I_Day_4
+// #Big_O_Time_O(n)_Space_O(1) #2023_12_09_Time_31_ms_(63.46%)_Space_20.5_MB_(81.73%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer
+     */
+    public function jump($nums) {
+        $length = 0;
+        $maxLength = 0;
+        $minJump = 0;
+        for ($i = 0; $i < count($nums) - 1; ++$i) {
+            $length--;
+            $maxLength--;
+            $maxLength = max($maxLength, $nums[$i]);
+            if ($length <= 0) {
+                $length = $maxLength;
+                $minJump++;
+            }
+            if ($length >= count($nums) - $i - 1) {
+                return $minJump;
+            }
+        }
+        return $minJump;
+    }
+}
diff --git a/src/main/php/g0001_0100/s0045_jump_game_ii/readme.md b/src/main/php/g0001_0100/s0045_jump_game_ii/readme.md
new file mode 100644
index 0000000..10a43da
--- /dev/null
+++ b/src/main/php/g0001_0100/s0045_jump_game_ii/readme.md
@@ -0,0 +1,30 @@
+45\. Jump Game II
+
+Medium
+
+Given an array of non-negative integers `nums`, you are initially positioned at the first index of the array.
+
+Each element in the array represents your maximum jump length at that position.
+
+Your goal is to reach the last index in the minimum number of jumps.
+
+You can assume that you can always reach the last index.
+
+**Example 1:**
+
+**Input:** nums = [2,3,1,1,4]
+
+**Output:** 2
+
+**Explanation:** The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1, then 3 steps to the last index. 
+
+**Example 2:**
+
+**Input:** nums = [2,3,0,1,4]
+
+**Output:** 2 
+
+**Constraints:**
+
+*   <code>1 <= nums.length <= 10<sup>4</sup></code>
+*   `0 <= nums[i] <= 1000`
\ No newline at end of file
diff --git a/src/main/php/g0001_0100/s0046_permutations/Solution.php b/src/main/php/g0001_0100/s0046_permutations/Solution.php
new file mode 100644
index 0000000..cddaddc
--- /dev/null
+++ b/src/main/php/g0001_0100/s0046_permutations/Solution.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace leetcode\g0001_0100\s0046_permutations;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Backtracking
+// #Algorithm_I_Day_11_Recursion_Backtracking #Level_2_Day_20_Brute_Force/Backtracking
+// #Udemy_Backtracking/Recursion #Big_O_Time_O(n*n!)_Space_O(n+n!)
+// #2023_12_09_Time_4_ms_(92.42%)_Space_19.2_MB_(92.42%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer[][]
+     */
+    public function permute($nums) {
+        if ($nums == null || count($nums) == 0) {
+            return array();
+        }
+        $finalResult = array();
+        $this->permuteRecur($nums, $finalResult, array(), array_fill(0, count($nums), false));
+        return $finalResult;
+    }
+
+    private function permuteRecur($nums, &$finalResult, $currResult, $used) {
+        if (count($currResult) == count($nums)) {
+            array_push($finalResult, $currResult);
+            return;
+        }
+        for ($i = 0; $i < count($nums); $i++) {
+            if ($used[$i]) {
+                continue;
+            }
+            array_push($currResult, $nums[$i]);
+            $used[$i] = true;
+            $this->permuteRecur($nums, $finalResult, $currResult, $used);
+            $used[$i] = false;
+            array_pop($currResult);
+        }
+    }
+}
diff --git a/src/main/php/g0001_0100/s0046_permutations/readme.md b/src/main/php/g0001_0100/s0046_permutations/readme.md
new file mode 100644
index 0000000..4d95634
--- /dev/null
+++ b/src/main/php/g0001_0100/s0046_permutations/readme.md
@@ -0,0 +1,29 @@
+46\. Permutations
+
+Medium
+
+Given an array `nums` of distinct integers, return _all the possible permutations_. You can return the answer in **any order**.
+
+**Example 1:**
+
+**Input:** nums = [1,2,3]
+
+**Output:** [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]] 
+
+**Example 2:**
+
+**Input:** nums = [0,1]
+
+**Output:** [[0,1],[1,0]] 
+
+**Example 3:**
+
+**Input:** nums = [1]
+
+**Output:** [[1]] 
+
+**Constraints:**
+
+*   `1 <= nums.length <= 6`
+*   `-10 <= nums[i] <= 10`
+*   All the integers of `nums` are **unique**.
\ No newline at end of file
diff --git a/src/test/php/g0001_0100/s0031_next_permutation/SolutionTest.php b/src/test/php/g0001_0100/s0031_next_permutation/SolutionTest.php
new file mode 100644
index 0000000..b301d11
--- /dev/null
+++ b/src/test/php/g0001_0100/s0031_next_permutation/SolutionTest.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace leetcode\g0001_0100\s0031_next_permutation;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testNextPermutation() {
+        $array = array(1, 2, 3);
+        (new Solution())->nextPermutation($array);
+        $this->assertEquals(array(1, 3, 2), $array);
+    }
+
+    public function testNextPermutation2() {
+        $array = array(3, 2, 1);
+        (new Solution())->nextPermutation($array);
+        $this->assertEquals(array(1, 2, 3), $array);
+    }
+
+    public function testNextPermutation3() {
+        $array = array(1, 1, 5);
+        (new Solution())->nextPermutation($array);
+        $this->assertEquals(array(1, 5, 1), $array);
+    }
+}
diff --git a/src/test/php/g0001_0100/s0032_longest_valid_parentheses/SolutionTest.php b/src/test/php/g0001_0100/s0032_longest_valid_parentheses/SolutionTest.php
new file mode 100644
index 0000000..c1e9633
--- /dev/null
+++ b/src/test/php/g0001_0100/s0032_longest_valid_parentheses/SolutionTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace leetcode\g0001_0100\s0032_longest_valid_parentheses;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testLongestValidParentheses() {
+        $this->assertEquals(2, (new Solution())->longestValidParentheses("(()"));
+    }
+
+    public function testLongestValidParentheses2() {
+        $this->assertEquals(4, (new Solution())->longestValidParentheses(")()())"));
+    }
+
+    public function testLongestValidParentheses3() {
+        $this->assertEquals(0, (new Solution())->longestValidParentheses(""));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0033_search_in_rotated_sorted_array/SolutionTest.php b/src/test/php/g0001_0100/s0033_search_in_rotated_sorted_array/SolutionTest.php
new file mode 100644
index 0000000..b98d778
--- /dev/null
+++ b/src/test/php/g0001_0100/s0033_search_in_rotated_sorted_array/SolutionTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace leetcode\g0001_0100\s0033_search_in_rotated_sorted_array;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testSearch() {
+        $this->assertEquals(4, (new Solution())->search(array(4, 5, 6, 7, 0, 1, 2), 0));
+    }
+
+    public function testSearch2() {
+        $this->assertEquals(-1, (new Solution())->search(array(4, 5, 6, 7, 0, 1, 2), 3));
+    }
+
+    public function testSearch3() {
+        $this->assertEquals(-1, (new Solution())->search(array(1), 0));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/SolutionTest.php b/src/test/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/SolutionTest.php
new file mode 100644
index 0000000..6cb4a3d
--- /dev/null
+++ b/src/test/php/g0001_0100/s0034_find_first_and_last_position_of_element_in_sorted_array/SolutionTest.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace leetcode\g0001_0100\s0034_find_first_and_last_position_of_element_in_sorted_array;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testSearchRange() {
+        $expected = array(3, 4);
+        $actual = (new Solution())->searchRange(array(5, 7, 7, 8, 8, 10), 8);
+        $this->assertEquals($expected, $actual);
+    }
+
+    public function testSearchRange2() {
+        $expected = array(-1, -1);
+        $actual = (new Solution())->searchRange(array(5, 7, 7, 8, 8, 10), 6);
+        $this->assertEquals($expected, $actual);
+    }
+
+    public function testSearchRange3() {
+        $expected = array(-1, -1);
+        $actual = (new Solution())->searchRange(array(), 0);
+        $this->assertEquals($expected, $actual);
+    }
+}
diff --git a/src/test/php/g0001_0100/s0035_search_insert_position/SolutionTest.php b/src/test/php/g0001_0100/s0035_search_insert_position/SolutionTest.php
new file mode 100644
index 0000000..f976437
--- /dev/null
+++ b/src/test/php/g0001_0100/s0035_search_insert_position/SolutionTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace leetcode\g0001_0100\s0035_search_insert_position;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testSearchInsert() {
+        $this->assertEquals(2, (new Solution())->searchInsert(array(1, 3, 5, 6), 5));
+    }
+
+    public function testSearchInsert2() {
+        $this->assertEquals(1, (new Solution())->searchInsert(array(1, 3, 5, 6), 2));
+    }
+
+    public function testSearchInsert3() {
+        $this->assertEquals(4, (new Solution())->searchInsert(array(1, 3, 5, 6), 7));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0039_combination_sum/SolutionTest.php b/src/test/php/g0001_0100/s0039_combination_sum/SolutionTest.php
new file mode 100644
index 0000000..908431f
--- /dev/null
+++ b/src/test/php/g0001_0100/s0039_combination_sum/SolutionTest.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace leetcode\g0001_0100\s0039_combination_sum;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testCombinationSum() {
+        $this->assertEquals(
+            array(array(7), array(3, 2, 2)),
+            (new Solution())->combinationSum(array(2, 3, 6, 7), 7)
+        );
+    }
+
+    public function testCombinationSum2() {
+        $this->assertEquals(
+            array(array(5, 3), array(3, 3, 2), array(2, 2, 2, 2)),
+            (new Solution())->combinationSum(array(2, 3, 5), 8)
+        );
+    }
+
+    public function testCombinationSum3() {
+        $this->assertEquals(
+            array(),
+            (new Solution())->combinationSum(array(2), 1)
+        );
+    }
+}
diff --git a/src/test/php/g0001_0100/s0041_first_missing_positive/SolutionTest.php b/src/test/php/g0001_0100/s0041_first_missing_positive/SolutionTest.php
new file mode 100644
index 0000000..3f16bdc
--- /dev/null
+++ b/src/test/php/g0001_0100/s0041_first_missing_positive/SolutionTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace leetcode\g0001_0100\s0041_first_missing_positive;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testFirstMissingPositive() {
+        $this->assertEquals(3, (new Solution())->firstMissingPositive(array(1, 2, 0)));
+    }
+
+    public function testFirstMissingPositive2() {
+        $this->assertEquals(2, (new Solution())->firstMissingPositive(array(3, 4, -1, 1)));
+    }
+
+    public function testFirstMissingPositive3() {
+        $this->assertEquals(1, (new Solution())->firstMissingPositive(array(7, 8, 9, 11, 12)));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0042_trapping_rain_water/SolutionTest.php b/src/test/php/g0001_0100/s0042_trapping_rain_water/SolutionTest.php
new file mode 100644
index 0000000..b52b94c
--- /dev/null
+++ b/src/test/php/g0001_0100/s0042_trapping_rain_water/SolutionTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace leetcode\g0001_0100\s0042_trapping_rain_water;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testTrap() {
+        $this->assertEquals(6, (new Solution())->trap(array(0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1)));
+    }
+
+    public function testTrap2() {
+        $this->assertEquals(9, (new Solution())->trap(array(4, 2, 0, 3, 2, 5)));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0045_jump_game_ii/SolutionTest.php b/src/test/php/g0001_0100/s0045_jump_game_ii/SolutionTest.php
new file mode 100644
index 0000000..5ef10a5
--- /dev/null
+++ b/src/test/php/g0001_0100/s0045_jump_game_ii/SolutionTest.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace leetcode\g0001_0100\s0045_jump_game_ii;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testJump() {
+        $this->assertEquals(2, (new Solution())->jump(array(2, 3, 1, 1, 4)));
+    }
+
+    public function testJump2() {
+        $this->assertEquals(2, (new Solution())->jump(array(2, 3, 0, 1, 4)));
+    }
+}
diff --git a/src/test/php/g0001_0100/s0046_permutations/SolutionTest.php b/src/test/php/g0001_0100/s0046_permutations/SolutionTest.php
new file mode 100644
index 0000000..b5b7628
--- /dev/null
+++ b/src/test/php/g0001_0100/s0046_permutations/SolutionTest.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace leetcode\g0001_0100\s0046_permutations;
+
+use PHPUnit\Framework\TestCase;
+
+class SolutionTest extends TestCase {
+    public function testPermute() {
+        $expected = array(array(1, 2, 3), array(1, 3, 2), array(2, 1, 3), array(2, 3, 1),
+            array(3, 1, 2), array(3, 2, 1));
+        $this->assertEquals($expected, (new Solution())->permute(array(1, 2, 3)));
+    }
+
+    public function testPermute2() {
+        $expected = array(array(0, 1), array(1, 0));
+        $this->assertEquals($expected, (new Solution())->permute(array(0, 1)));
+    }
+
+    public function testPermute3() {
+        $expected = array(array(1));
+        $this->assertEquals($expected, (new Solution())->permute(array(1)));
+    }
+}