Added tasks 11-25

src/main/php/g0001_0100/s0011_container_with_most_water/Solution.php

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+<?php
+
+namespace leetcode\g0001_0100\s0011_container_with_most_water;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Greedy #Two_Pointers
+// #Algorithm_II_Day_4_Two_Pointers #Big_O_Time_O(n)_Space_O(1)
+// #2023_12_07_Time_177_ms_(88.58%)_Space_31.7_MB_(66.67%)
+
+class Solution {
+    /**
+     * @param Integer[] $height
+     * @return Integer
+     */
+    public function maxArea($height) {
+        $maxArea = -1;
+        $left = 0;
+        $right = count($height) - 1;
+        while ($left < $right) {
+            if ($height[$left] < $height[$right]) {
+                $maxArea = max($maxArea, $height[$left] * ($right - $left));
+                $left++;
+            } else {
+                $maxArea = max($maxArea, $height[$right] * ($right - $left));
+                $right--;
+            }
+        }
+        return $maxArea;
+    }
+}

src/main/php/g0001_0100/s0011_container_with_most_water/readme.md

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+11\. Container With Most Water
+
+Medium
+
+Given `n` non-negative integers <code>a<sub>1</sub>, a<sub>2</sub>, ..., a<sub>n</sub></code> , where each represents a point at coordinate <code>(i, a<sub>i</sub>)</code>. `n` vertical lines are drawn such that the two endpoints of the line `i` is at <code>(i, a<sub>i</sub>)</code> and `(i, 0)`. Find two lines, which, together with the x-axis forms a container, such that the container contains the most water.
+
+**Notice** that you may not slant the container.
+
+**Example 1:**
+
+![](https://s3-lc-upload.s3.amazonaws.com/uploads/2018/07/17/question_11.jpg)
+
+**Input:** height = [1,8,6,2,5,4,8,3,7]
+
+**Output:** 49
+
+**Explanation:** The above vertical lines are represented by array [1,8,6,2,5,4,8,3,7]. In this case, the max area of water (blue section) the container can contain is 49. 
+
+**Example 2:**
+
+**Input:** height = [1,1]
+
+**Output:** 1 
+
+**Example 3:**
+
+**Input:** height = [4,3,2,1,4]
+
+**Output:** 16 
+
+**Example 4:**
+
+**Input:** height = [1,2,1]
+
+**Output:** 2 
+
+**Constraints:**
+
+*   `n == height.length`
+*   <code>2 <= n <= 10<sup>5</sup></code>
+*   <code>0 <= height[i] <= 10<sup>4</sup></code>

src/main/php/g0001_0100/s0015_3sum/Solution.php

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+<?php
+
+namespace leetcode\g0001_0100\s0015_3sum;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Sorting #Two_Pointers
+// #Data_Structure_II_Day_1_Array #Algorithm_II_Day_3_Two_Pointers #Udemy_Two_Pointers
+// #Big_O_Time_O(n^2)_Space_O(1) #Big_O_Time_O(n*log(n))_Space_O(n^2)
+// #2023_12_07_Time_252_ms_(77.94%)_Space_28.5_MB_(94.12%)
+
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer[][]
+     */
+    public function threeSum($nums) {
+        sort($nums);
+        $len = count($nums);
+        $result = [];
+        for ($i = 0; $i < $len - 2; $i++) {
+            $l = $i + 1;
+            $r = $len - 1;
+            while ($r > $l) {
+                $sum = $nums[$i] + $nums[$l] + $nums[$r];
+                if ($sum < 0) {
+                    $l++;
+                } elseif ($sum > 0) {
+                    $r--;
+                } else {
+                    $list = [$nums[$i], $nums[$l], $nums[$r]];
+                    $result[] = $list;
+                    while ($l < $r && $nums[$l + 1] == $nums[$l]) {
+                        $l++;
+                    }
+                    while ($r > $l && $nums[$r - 1] == $nums[$r]) {
+                        $r--;
+                    }
+                    $l++;
+                    $r--;
+                }
+            }
+            while ($i < $len - 1 && $nums[$i + 1] == $nums[$i]) {
+                $i++;
+            }
+        }
+        return $result;
+    }
+}

src/main/php/g0001_0100/s0015_3sum/readme.md

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+15\. 3Sum
+
+Medium
+
+Given an integer array nums, return all the triplets `[nums[i], nums[j], nums[k]]` such that `i != j`, `i != k`, and `j != k`, and `nums[i] + nums[j] + nums[k] == 0`.
+
+Notice that the solution set must not contain duplicate triplets.
+
+**Example 1:**
+
+**Input:** nums = [-1,0,1,2,-1,-4]
+
+**Output:** [[-1,-1,2],[-1,0,1]] 
+
+**Example 2:**
+
+**Input:** nums = []
+
+**Output:** [] 
+
+**Example 3:**
+
+**Input:** nums = [0]
+
+**Output:** [] 
+
+**Constraints:**
+
+*   `0 <= nums.length <= 3000`
+*   <code>-10<sup>5</sup> <= nums[i] <= 10<sup>5</sup></code>

src/main/php/g0001_0100/s0017_letter_combinations_of_a_phone_number/Solution.php

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+<?php
+
+namespace leetcode\g0001_0100\s0017_letter_combinations_of_a_phone_number;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #String #Hash_Table #Backtracking
+// #Algorithm_II_Day_11_Recursion_Backtracking #Udemy_Backtracking/Recursion
+// #Big_O_Time_O(4^n)_Space_O(n) #2023_12_07_Time_5_ms_(60.19%)_Space_19.1_MB_(59.26%)
+
+class Solution {
+    /**
+     * @param String $digits
+     * @return String[]
+     */
+    public function letterCombinations($digits) {
+        if (empty($digits)) {
+            return [];
+        }
+        $letters = ["", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"];
+        $ans = [];
+        $curr = '';
+        $this->findCombinations(0, $digits, $letters, $curr, $ans);
+        return $ans;
+    }
+
+    private function findCombinations($start, $nums, $letters, &$curr, &$ans) {
+        if (strlen($curr) == strlen($nums)) {
+            $ans[] = $curr;
+            return;
+        }
+        for ($i = $start; $i < strlen($nums); $i++) {
+            $n = intval($nums[$i]);
+            for ($j = 0; $j < strlen($letters[$n]); $j++) {
+                $ch = $letters[$n][$j];
+                $curr .= $ch;
+                $this->findCombinations($i + 1, $nums, $letters, $curr, $ans);
+                $curr = substr($curr, 0, -1);
+            }
+        }
+    }
+}

src/main/php/g0001_0100/s0017_letter_combinations_of_a_phone_number/readme.md

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+17\. Letter Combinations of a Phone Number
+
+Medium
+
+Given a string containing digits from `2-9` inclusive, return all possible letter combinations that the number could represent. Return the answer in **any order**.
+
+A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.
+
+![](https://upload.wikimedia.org/wikipedia/commons/thumb/7/73/Telephone-keypad2.svg/200px-Telephone-keypad2.svg.png)
+
+**Example 1:**
+
+**Input:** digits = "23"
+
+**Output:** ["ad","ae","af","bd","be","bf","cd","ce","cf"] 
+
+**Example 2:**
+
+**Input:** digits = ""
+
+**Output:** [] 
+
+**Example 3:**
+
+**Input:** digits = "2"
+
+**Output:** ["a","b","c"] 
+
+**Constraints:**
+
+*   `0 <= digits.length <= 4`
+*   `digits[i]` is a digit in the range `['2', '9']`.

src/main/php/g0001_0100/s0019_remove_nth_node_from_end_of_list/Solution.php

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+<?php
+
+namespace leetcode\g0001_0100\s0019_remove_nth_node_from_end_of_list;
+
+// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Two_Pointers #Linked_List
+// #Algorithm_I_Day_5_Two_Pointers #Level_2_Day_3_Linked_List #Big_O_Time_O(L)_Space_O(L)
+// #2023_12_07_Time_4_ms_(81.93%)_Space_18.9_MB_(91.57%)
+
+use leetcode\com_github_leetcode\ListNode;
+
+/*
+ * 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 {
+    private $n;
+
+    public function removeNthFromEnd($head, $n) {
+        $this->n = $n;
+        $node = new ListNode(0, $head);
+        $this->removeNth($node);
+        return $node->next;
+    }
+
+    private function removeNth($node) {
+        if ($node->next === null) {
+            return;
+        }
+        $this->removeNth($node->next);
+        $this->n--;
+        if ($this->n == 0) {
+            $node->next = $node->next->next;
+        }
+    }
+}

src/main/php/g0001_0100/s0019_remove_nth_node_from_end_of_list/readme.md

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+19\. Remove Nth Node From End of List
+
+Medium
+
+Given the `head` of a linked list, remove the `nth` node from the end of the list and return its head.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/10/03/remove_ex1.jpg)
+
+**Input:** head = [1,2,3,4,5], n = 2
+
+**Output:** [1,2,3,5] 
+
+**Example 2:**
+
+**Input:** head = [1], n = 1
+
+**Output:** [] 
+
+**Example 3:**
+
+**Input:** head = [1,2], n = 1
+
+**Output:** [1] 
+
+**Constraints:**
+
+*   The number of nodes in the list is `sz`.
+*   `1 <= sz <= 30`
+*   `0 <= Node.val <= 100`
+*   `1 <= n <= sz`
+
+**Follow up:** Could you do this in one pass?

src/main/php/g0001_0100/s0020_valid_parentheses/Solution.php

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+<?php
+
+namespace leetcode\g0001_0100\s0020_valid_parentheses;
+
+// #Easy #Top_100_Liked_Questions #Top_Interview_Questions #String #Stack
+// #Data_Structure_I_Day_9_Stack_Queue #Udemy_Strings #Big_O_Time_O(n)_Space_O(n)
+// #2023_12_07_Time_3_ms_(88.14%)_Space_19.1_MB_(76.99%)
+
+class Solution {
+    /**
+     * @param String $s
+     * @return Boolean
+     */
+    public function isValid($s) {
+        $stack = [];
+        $length = strlen($s);
+        for ($i = 0; $i < $length; $i++) {
+            $c = $s[$i];
+            if ($c == '(' || $c == '[' || $c == '{') {
+                array_push($stack, $c);
+            } elseif (($c == ')' && !empty($stack) && end($stack) == '(')
+                || ($c == '}' && !empty($stack) && end($stack) == '{')
+                || ($c == ']' && !empty($stack) && end($stack) == '[')
+            ) {
+                array_pop($stack);
+            } else {
+                return false;
+            }
+        }
+        return empty($stack);
+    }
+}

src/main/php/g0001_0100/s0020_valid_parentheses/readme.md

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+20\. Valid Parentheses
+
+Easy
+
+Given a string `s` containing just the characters `'('`, `')'`, `'{'`, `'}'`, `'['` and `']'`, determine if the input string is valid.
+
+An input string is valid if:
+
+1.  Open brackets must be closed by the same type of brackets.
+2.  Open brackets must be closed in the correct order.
+
+**Example 1:**
+
+**Input:** s = "()"
+
+**Output:** true 
+
+**Example 2:**
+
+**Input:** s = "()[]{}"
+
+**Output:** true 
+
+**Example 3:**
+
+**Input:** s = "(]"
+
+**Output:** false 
+
+**Example 4:**
+
+**Input:** s = "([)]"
+
+**Output:** false 
+
+**Example 5:**
+
+**Input:** s = "{[]}"
+
+**Output:** true 
+
+**Constraints:**
+
+*   <code>1 <= s.length <= 10<sup>4</sup></code>
+*   `s` consists of parentheses only `'()[]{}'`.