LeetCode 017. 电话号码的字母组合  dfs

给定一个仅包含数字 2-9 的字符串，返回所有它能表示的字母组合。

给出数字到字母的映射如下（与电话按键相同）。注意 1 不对应任何字母。


示例:

输入："23"
输出：["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

class Solution {
public:

    map<char, string> m = {
    {‘2‘,"abc"},{‘3‘,"def"},
    {‘4‘,"ghi"},{‘5‘,"jkl"},
    {‘6‘,"mno"},{‘7‘,"pqrs"},
    {‘8‘,"tuv"},{‘9‘,"wxyz"}
};

vector<string> ans;

void dfs(string s, string digits, int idx)
{
    if (idx == digits.size()) {
        ans.push_back(s);
        return;
    }
    char digt = digits[idx];
    for (int j = 0; j < m[digt].size(); j++) {
        s += m[digt][j];
        dfs(s, digits,idx + 1);
        s.pop_back();
    }
}

vector<string> letterCombinations(string digits) {
    if(digits.size() == 0) return vector<string> ();
    string s;
    dfs(s, digits, 0);

    return ans;
}


};