Added tasks 169-226

src/main/php/g0101_0200/s0169_majority_element/Solution.php

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+<?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;
+            }
+        }
+    }
+}

src/main/php/g0101_0200/s0169_majority_element/readme.md

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+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?

src/main/php/g0101_0200/s0189_rotate_array/Solution.php

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+<?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);
+    }
+}

src/main/php/g0101_0200/s0189_rotate_array/readme.md

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+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?

src/main/php/g0101_0200/s0198_house_robber/Solution.php

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+<?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];
+    }
+}

src/main/php/g0101_0200/s0198_house_robber/readme.md

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+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`

src/main/php/g0101_0200/s0200_number_of_islands/Solution.php

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+<?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);
+    }
+}

src/main/php/g0101_0200/s0200_number_of_islands/readme.md

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+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'`.

src/main/php/g0201_0300/s0206_reverse_linked_list/Solution.php

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+<?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;
+    }
+}

src/main/php/g0201_0300/s0206_reverse_linked_list/readme.md

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+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?