Add phoneNumberLetterPermutations script

phoneNumberLetterPermutations.php

@@ -0,0 +1,49 @@
+<?php
+
+
+class Solution
+{
+    const letters = [
+        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']
+    ];
+
+    /**
+     * @param mixed $digits
+     * @access public
+     * @return array
+     */
+    public static function letterCombinations($digits): array
+    {
+        if ($digits === '') {
+            return [];
+        }
+
+        $lookupResult = [];
+        $x = 0;
+        while (count($lookupResult) === 0) {
+            $lookupResult = self::letters[$digits[$x]] ?? [];
+            $x++;
+        }
+
+        for ($i = 1; $i < strlen($digits); $i++) {
+            $temp = [];
+
+            foreach (self::letters[$digits[$i]] as $char) {
+                foreach ($lookupResult as $r) {
+                    $temp[] = $r . $char;
+                }
+            }
+
+            $lookupResult = $temp;
+        }
+        return $lookupResult;
+    }
+
+}