leetcode_17电话号码的组合

1. 题意

输出电话号码对应的字母左右组合
电话号码的组合

2. 题解

回溯

class Solution {
public:void gen_res(vector<string> &res, vector<string> &s_m,string &digits, string &t, size_t depth) {if (depth == digits.size()) {if ( !t.empty())res.push_back(t);return ;}int k = digits[depth] - '0';int k_len = s_m[k].size();for ( int i = 0;i < k_len; ++i) {t.push_back(s_m[k][i]);gen_res(res, s_m, digits, t, depth + 1);t.pop_back();}}vector<string> letterCombinations(string digits) {vector<string> s_m = { "","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};vector<string> res;string t;gen_res(res, s_m, digits, t, 0 );return res;}
};