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"].

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

每个数字代表一个种类，每个种类中有多个值，要求在每个种类中都选一个，所组成的所有不同的组合。

class Solution {
public:
   void dfs(vector<string>& re, int cur_dep,string& cur_re, string digits){
		static string tel_board[] = {
			"0", "1", "abc", "def", "ghi", 
			"jkl", "mno", "pqrs", "tuv", "wxyz", };
		if(cur_dep == digits.length()){
			re.push_back(cur_re);
			return;
		}
		string cur_str = tel_board[digits[cur_dep] - ‘0‘];
		for (int i = 0; i < cur_str.length(); ++i)
		{
			cur_re.push_back(cur_str[i]);
			dfs(re, cur_dep + 1, cur_re, digits);
			cur_re.pop_back();
		}
		
	}
	vector<string> letterCombinations(string digits) {
		vector<string> re;
		string cur_re("");
		dfs(re, 0, cur_re, digits);
		return re;

	}
};

Letter Combinations of a Phone Number

原文：http://blog.csdn.net/shiquxinkong/article/details/18676713