feat: 每日一题2019-06-18参考答案

README.en.md

@@ -80,9 +80,9 @@ The data structures mainly includes:
 
 ## Top Problems Progress
 
-- [Top 100 Liked Questions](https://leetcode.com/problemset/top-100-liked-questions/) (63 / 100)
+- [Top 100 Liked Questions](https://leetcode.com/problemset/top-100-liked-questions/) (67 / 100)
 
-- [Top Interview Questions](https://leetcode.com/problemset/top-interview-questions/) (85 / 145)
+- [Top Interview Questions](https://leetcode.com/problemset/top-interview-questions/) (88 / 145)
 
 
 

README.md

@@ -83,9 +83,9 @@ leetcode 题解，记录自己的 leetcode 解题之路。
 
 ## Top题目进度
 
-- [Top 100 Liked Questions](https://leetcode.com/problemset/top-100-liked-questions/) (63 / 100)
+- [Top 100 Liked Questions](https://leetcode.com/problemset/top-100-liked-questions/) (67 / 100)
 
-- [Top Interview Questions](https://leetcode.com/problemset/top-interview-questions/) (85 / 145)
+- [Top Interview Questions](https://leetcode.com/problemset/top-interview-questions/) (88 / 145)
 ## 传送门
 
 ### leetcode 经典题目的解析

daily/answers/17.letter-combinations-of-a-phone-number.js

@@ -0,0 +1,44 @@
+/*
+ * @lc app=leetcode id=17 lang=javascript
+ *
+ * [17] Letter Combinations of a Phone Number
+ */
+function backtrack(list, tempList, digits, start, keys) {
+  if (tempList.length === digits.length) {
+    return list.push(tempList.join(''));
+  }
+
+  for (let i = start; i < digits.length; i++) {
+    const chars = keys[digits[i]];
+    for (let j = 0; j < chars.length; j++) {
+      tempList.push(chars[j]);
+      backtrack(list, tempList, digits, i + 1, keys);
+      tempList.pop();
+    }
+  }
+}
+/**
+ * @param {string} digits
+ * @return {string[]}
+ */
+var letterCombinations = function(digits) {
+  if (digits.length === 0) return [];
+  // Input:Digit string "23"
+  // Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
+  const keys = [
+    "",
+    "",
+    "abc",
+    "def",
+    "ghi",
+    "jkl",
+    "mno",
+    "pqrs",
+    "tuv",
+    "wxyz"
+  ];
+
+  const list = [];
+  backtrack(list, [], digits, 0, keys);
+  return list;
+};