Letter Combination of a phone number

void fun(string digits,unordered_map<char,string> mp,vector<string> &ans,string cur,int i,int n){
     if(i<n){
         for(int k=0;k<mp[digits[i]].size();k++){
            fun(digits,mp,ans,cur+mp[digits[i]][k],i+1,n);
         }
     }
     else{
         ans.push_back(cur);
         return;
     }
}

class Solution {
public:
    vector<string> letterCombinations(string digits) {
        vector <string> ans;
        if(digits.size()==0) return ans;
        unordered_map<char,string> mp;
        mp['2']="abc";
        mp['3']="def";
        mp['4']="ghi";
        mp['5']="jkl";
        mp['6']="mno";
        mp['7']="pqrs";
        mp['8']="tuv";
        mp['9']="wxyz";

        fun(digits,mp,ans,"",0,digits.size());
        return ans;
    }
};

#Python
ans=[]
def fun(st,i,cur):
    print(i,len(st))
    global ans;
    dict={'2':'abc','3':'def','4':'ghi','5':'jkl','6':'mno','7':'pqrs','8':'tuv','9':'wxyz'}
    if i==len(st):
        ans.append(cur)
        return
    else:
        temp=dict[st[i]]
        for k in range(len(temp)):
            fun(st,i+1,cur+temp[k])

class Solution:
    def letterCombinations(self, digits: str) -> List[str]:
        if len(digits)==0:
            return []
        global ans;
        ans=[]
        fun(digits,0,'')
        return ans;