codeforces - accurate lee

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define fast()(ios_base::sync_with_stdio(0),cin.tie(NULL));
int main()
{
    fast();
    ll t;
    cin>>t;
    while(t--)
    {
        ll n;
        cin>>n;
        string s,sub,x;
        cin>>s;
        ll i;
        for(i=n-1;i>=0;i--)
        {
            if(i==n-1 && s[i]=='1')
            {
                while(s[i]=='1')
                {
                    x.push_back(s[i]);
                    i--;
                }
                i++;
            }
            else
            {
                if(s[i]=='0')sub.push_back(s[i]);
                else
                {
                    if(sub.size()>0)
                    {
                        sub.clear();
                        sub.push_back('0');
                    }
                }
            }
        }
        x+=sub;
        for(i=x.size()-1;i>=0;i--)cout<<x[i];
        cout<<endl;

    }
}