My submissions are showing not being judged

why my submissions are showing not being judged

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent.

my code;

#include <bits/stdc++.h>
using namespace std;

class Solution {
private:

std::array<std::string, 10> mappings = {“0”, “1”, “abc”, “def”, “ghi”, “jkl”, “mno”, “pqrs”, “tuv”, “wxyz”};

std::string getLettersMapping(char digit) {
return mappings[digit - ‘0’];
}

void dfs(std::vectorstd::string &combinations, std::string digits, std::string &s) {
if (digits.empty()) {
combinations.push_back(s);
return;
}

auto letters = getLettersMapping(digits.front());

for (const auto &ch : letters) {
    s.push_back(ch);
    dfs(combinations, digits.substr(1), s);
    s.pop_back();
}

}

public:
std::vectorstd::string letterCombinations(std::string digits) {

std::vector<std::string> ans;
if (digits.empty() || digits.size() == 0) {
  return ans;
}
std::string s;
dfs(ans, digits, s);
return ans;

}
};
int main(){
string s;
cin>>s;
Solution s1;
vectorans;
ans=s1.letterCombinations(s);
for(int i=0;i<ans.size();i++){
cout<<ans[i]<<endl;
}
}