leetcode题解-17.电话号码的数字组合

电话号码的数字组合:link

1.题目分析

组合方式随着数字的增多是呈现为树状发散的方式，主要就是代码实现了。

2.示例代码

class Solution {
public:
	vector<string> letterCombinations(string digits) {
		map<char, string> num2characters = { {'1', ""}, {'2', "abc"},{'3', "edf"},
											{'4', "ghi"}, {'5', "jkl"},{'6', "mno"},
		    								{'7', "pqrs"}, {'8', "tuv"},{'9', "wxyz"}};
        
		vector<string> ret;
        if(digits.empty())
            return ret;
        ret.push_back("");
		for (char c : digits) {
			vector<string> tmp;
			string cur = num2characters[c];
			for (string str : ret) {
				for (int i = 0; i < cur.size(); ++i) {
					tmp.push_back(str + cur.substr(i, 1));
				}
			}
			ret = tmp;
		}
		
		return ret;
	}
};