【LeetCode】 17. 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.

题目大意就是按手机上数字键，能组成多种字母组合，如“23”，2上面有abc 3上面有def，故可以组成

"ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"

这样的组合。

代码：

class Solution {private:    string num[10]={"","","abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};        vector<string> str;public:    void dfs(const string& digits,int l,string s){        int n=digits[l]-'0';        if (digits.size()==s.size()){            str.push_back(s);            return;        }        for(int i=0;i<num[n].size();++i)            dfs(digits,l+1,s+num[n][i]);    }    vector<string> letterCombinations(string digits) {        if (digits.size()==0) return str;        dfs(digits,0,"");        return str;    }};

从代码长度上来看比其他Medium的题目短不少，调试起来也不难，主要是想到用深度搜索的方法去解答。