#include <bits/stdc++.h>   using namespace std;   const long long mod = 1000000007;   const int inf = 1e9 + 10;   const long long INF = 1e18;   const long double EPS = 1e-10;   const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};   const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};   template <class T>   bool chmax(T &a, const T &b) {     if (a < b) {       a = b;       return 1;     }     return 0;   }   template <class T>   bool chmin(T &a, const T &b) {     if (a > b) {       a = b;       return 1;     }     return 0;   }   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout << fixed << setprecision(25);     int t;     cin >> t;     while (t--) {       int n;       string s;       cin >> n >> s;       string ans =   ;       int idx = 0;       while (idx < n && s[idx] ==  0 ) {         ans += s[idx];         idx++;       }       s = s.substr(idx);       reverse(s.begin(), s.end());       n = s.size();       string ans2 =   ;       idx = 0;       while (idx < n && s[idx] ==  1 ) {         ans2 += s[idx];         idx++;       }       s = s.substr(idx);       n = s.size();       if (n) ans +=  0 ;       ans += ans2;       cout << ans <<   n ;     }     return 0;   }   