leetcode 17

Author: geekplux

README.md

@@ -33,6 +33,7 @@
 - 14.Longest Common Prefix `easy` `string` [link](https://leetcode.com/problems/longest-common-prefix/description/) [code](./leetcode/14.js)
 - 15.3Sum `medium` `array` [link](https://leetcode.com/problems/3sum/) [code](./leetcode/15.js)
 - 16.3Sum Closest `medium` `array` [link](https://leetcode.com/problems/3sum-closest/) [code](./leetcode/16.js)
+- 17.Letter Combinations of a Phone Number `medium` `string` [link](https://leetcode.com/problems/letter-combinations-of-a-phone-number/) [code](./leetcode/17.js)
 
 ## lintcode
 

leetcode/17.js

@@ -0,0 +1,55 @@
+/*
+17. Letter Combinations of a Phone Number
+
+Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent.
+
+A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.
+
+
+
+Example:
+
+Input: "23"
+Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
+
+Note:
+Although the above answer is in lexicographical order, your answer could be in any order you want.
+*/
+
+
+/**
+ * @param {string} digits
+ * @return {string[]}
+ */
+var letterCombinations = function(digits) {
+  const letterMap = {
+    2: 'abc',
+    3: 'def',
+    4: 'ghi',
+    5: 'jkl',
+    6: 'mno',
+    7: 'pqrs',
+    8: 'tuv',
+    9: 'wxyz',
+  };
+
+  const nums = digits.split('');
+  let res = [];
+
+  const len = nums.length;
+  if (!len) return res;
+  if (len <= 1) {
+    return letterMap[nums[0]].split('');
+  }
+
+  let arr1 = letterCombinations(digits.substring(0, 1));
+  let arr2 = letterCombinations(digits.substring(1));
+
+  for (let i = 0; i < arr1.length; i++) {
+    for (let j = 0; j < arr2.length; j++) {
+      res.push(arr1[i] + arr2[j]);
+    }
+  }
+
+  return res;
+};