Letter Combinations of a Phone Number

最新推荐文章于 2025-07-20 11:42:00 发布

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本文介绍了一种算法，该算法能够根据电话按键上数字到字母的映射，输入一个数字字符串并返回所有可能的字母组合。通过深度优先搜索(DFS)递归地构建所有可能的组合。

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.

Example:

Input:Digit string "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

Code:

class Solution {
public:
    map<char,vector<char>> dict;
    vector<string> ret;
    void CreateDict()
    {
        dict.clear();
        dict['2'].push_back('a');
        dict['2'].push_back('b');
        dict['2'].push_back('c');
        dict['3'].push_back('d');
        dict['3'].push_back('e');
        dict['3'].push_back('f');
        dict['4'].push_back('g');
        dict['4'].push_back('h');
        dict['4'].push_back('i');
        dict['5'].push_back('j');
        dict['5'].push_back('k');
        dict['5'].push_back('l');
        dict['6'].push_back('m');
        dict['6'].push_back('n');
        dict['6'].push_back('o');
        dict['7'].push_back('p');
        dict['7'].push_back('q');
        dict['7'].push_back('r');
        dict['7'].push_back('s');
        dict['8'].push_back('t');
        dict['8'].push_back('u');
        dict['8'].push_back('v');
        dict['9'].push_back('w');
        dict['9'].push_back('x');
        dict['9'].push_back('y');
        dict['9'].push_back('z');


    }
    
    void DFS(int curDep,int len,string &s,string ans)
    {
        if(curDep==len)
        {
            ret.push_back(ans);
            return ;
        }
        for(int i=0;i<dict[s[curDep]].size();i++)
            DFS(curDep+1,len,s,ans+dict[s[curDep]][i]);
    }
    
    vector<string> letterCombinations(string digits) {
        ret.clear();
        CreateDict();
        DFS(0,digits.size(),digits,"");
        return ret;
    }
};