[Leetcode] Letter Combinations of a Phone Number

Given a digit string, 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.

Input:Digit string "23"

Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

模拟！

 1 class Solution {

 2 public:

 3     string key[10];

 4     void initKey() {

 5         key[0] = " ";

 6         key[1] = "";

 7         key[2] = "abc";

 8         key[3] = "def";

 9         key[4] = "ghi";

10         key[5] = "jkl";

11         key[6] = "mno";

12         key[7] = "pqrs";

13         key[8] = "tuv";

14         key[9] = "wxyz";

15     }

16     void findNext(vector<string> &res, string &digits, string s, int idx) {

17         if (s.length() == digits.length()) {

18             res.push_back(s);

19             return;

20         }

21         int k = digits[idx] - '0';

22         for (int i = 0; i < key[k].length(); ++i) {

23             findNext(res, digits, s + key[k][i], idx + 1);

24         }

25     }

26     vector<string> letterCombinations(string digits) {

27         initKey();

28         vector<string> res;

29         string s;

30         findNext(res, digits, s, 0);

31         return res;

32     }

33 };