HW14

index.php

@@ -0,0 +1,87 @@
+<?php
+/**
+ * Definition for a singly-linked list.
+ * class ListNode {
+ *     public $val = 0;
+ *     public $next = null;
+ *     function __construct($val) { $this->val = $val; }
+ * }
+ */
+
+class Solution
+{
+    /**
+     * @param ListNode $head
+     * @return Boolean
+     */
+    function hasCycle($head)
+    {
+        if ($head == null || $head->next == null) {
+            return false;
+        }
+
+        $slow = $head;
+        $fast = $head->next;
+
+        while ($slow != $fast) {
+
+            if ($fast == null || $fast->next == null) {
+                return false;
+            }
+
+            $slow = $slow->next;
+            $fast = $fast->next->next;
+        }
+
+        return true;
+    }
+}
+
+
+class Solution2
+{
+
+    /**
+     * @param String $digits
+     * @return String[]
+     */
+    function letterCombinations($digits)
+    {
+        if (empty($digits)) {
+            return []; // возвращаем пустой массив для пустой строки ввода
+        }
+
+        $digitMap = [
+            '2' => ['a', 'b', 'c'],
+            '3' => ['d', 'e', 'f'],
+            '4' => ['g', 'h', 'i'],
+            '5' => ['j', 'k', 'l'],
+            '6' => ['m', 'n', 'o'],
+            '7' => ['p', 'q', 'r', 's'],
+            '8' => ['t', 'u', 'v'],
+            '9' => ['w', 'x', 'y', 'z'],
+        ];
+
+        $result = [];
+        $currentCombination = '';
+
+        $this->generateCombinations($digits, 0, $digitMap, $currentCombination, $result);
+
+        return $result;
+    }
+
+    function generateCombinations($digits, $index, $digitMap, $currentCombination, &$result)
+    {
+        if ($index == strlen($digits)) {
+            $result[] = $currentCombination;
+            return;
+        }
+
+        $currentDigit = $digits[$index];
+        $letters = $digitMap[$currentDigit];
+
+        foreach ($letters as $letter) {
+            $this->generateCombinations($digits, $index + 1, $digitMap, $currentCombination . $letter, $result);
+        }
+    }
+}