C++ :

#include <bits/stdc++.h>

using namespace std;




int main(){
    int n, m;
    string a, b;
    cin >> n;
    for(int k=0;k<n;k++){
        b = "";
        cin >> m >> a;
        for(int i=m-1;i>=0;i--){
            if (a[i] == '0'){
                b = char( (a[i-2]-'0')*10+a[i-1]-'0'-1+'a')+b;
                i -= 2;
            }
            else{
                b = char(a[i]-'0' + 'a'-1)+b;
            }
        }
        cout << b << endl;
    }

}