Letter Combinations of a Phone Number

难度：1

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.

解法：

DFS裸搜

注意细节。。

class Solution 
{
public:
	vector<string>ans;
	string tmp;
	string s;
	int len_s;
	string Map[10]={"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
	void dfs(int x)//tmp
	{
		if(x == len_s)
		{
			ans.push_back(tmp);
			return;
		}
		//Map[s[x]-'0']
		for(int i=0;i<Map[s[x]-'0'].size();i++)
		{
			tmp+=Map[s[x]-'0'][i];
			dfs(x+1);
			tmp.pop_back();
		}
	}
    vector<string> letterCombinations(string digits) 
	{
		ans.clear();
		tmp="";
		s=digits;
		len_s=s.size();
		dfs(0);
		return ans;
    }
};