This is my CPP solution.
class Solution {
public:
string freqAlphabets(string s) {
int n = s.size();
unordered_map<char,char> ai_map;
for(int i=0;i<9;i++){
ai_map['1'+i] = 'a'+i;
}
unordered_map<string,char> jz_map;
for(int i=10;i<=26;i++){
string res = to_string(i);
res.push_back('#');
jz_map[res] = 'a' + i -1;
}
string ans = "";
int i = 0;
while(i<n){
if(i<n-2 && s[i+2] == '#'){
string part(s.begin()+i,s.begin()+i+3);
ans += jz_map[part];
i+=3;
}
else{
ans.push_back(ai_map[s[i]]);
i++;
}
}
return ans;
}
};