LeetCode 17. *的字母组合

题目描述链接：https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/

基本思路：dfs搜索即可。

LeetCode C++求解代码：

class Solution {
public:
    vector<string>res;
    unordered_map<char,string>fun;
    unordered_set<string>record;
    vector<string> letterCombinations(string digits) {
        
         fun['2']="abc";
         fun['3']="def";
         fun['4']="ghi";
         fun['5']="jkl";
         fun['6']="mno";
         fun['7']="pqrs";
         fun['8']="tuv";
         fun['9']="wxyz";
         string ans="";
         for(int i=0;i<fun[digits[0]].size();i++)
            dfs(digits,0,i,ans);
         return res;
         
    }
    void dfs(string digits,int i,int j,string ans){
        if(i==digits.size()-1&&ans.size()==digits.size()-1){
            
            ans+=fun[digits[i]][j];
            if(record.find(ans)==record.end()){
                
                  res.push_back(ans);
                  record.insert(ans);
            }
            return;
        }
        
        ans+=fun[digits[i]][j];
       
        for(int x=i+1;x<digits.size();x++){
            for(int y=0;y<fun[digits[x]].size();y++){ 
                dfs(digits,x,y,ans);
            }
        }
        ans.pop_back();
       

    }




};