题目连接

  

Letter Combinations of a Phone Number

Description

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"].

Note:

Although the above answer is in lexicographical order, your answer could be in any order you want.

dfs。。

class Solution {public:	vector
     
       letterCombinations(string digits) {		init();		ans.clear();		n = digits.length();		if (!n) return ans;		dfs(0, "", digits);		return ans;	}private:	size_t n;	map
      
        A;	vector
       
        ans;	void init() {		A[2] = "abc";		A[3] = "def";		A[4] = "ghi";		A[5] = "jkl";		A[6] = "mno";		A[7] = "pqrs";		A[8] = "tuv";		A[9] = "wxyz";	}	void dfs(int cur, string x, string digits) {		if (cur == n) { ans.push_back(x); return; }		int d = digits[cur] - '0';		for (size_t i = 0; i < A[d].size(); i++) {			dfs(cur + 1, x + A[d][i], digits);		}	}};