#include<iostream>

#include<string.h>

#include<string>

#include<algorithm>

using namespace std;

string a,b;

int vis[];

int main()

{

    int t;

    cin>>t;

    while(t--)

    {

        int n;

        cin>>n;

        cin>>a;

        b=a;

        memset(vis,,sizeof(vis));

        sort(b.begin(),b.end());

        int pos1=n-;

        for(int i=n-;i>=;i--)

        {

            if(b[pos1]==a[i])

            {

                vis[i]=;

                pos1--;

            }

        }

        pos1=pos1+;

        int pos2=;

        for(int i=;i<n;i++)

        {

            if(vis[i]==&&a[i]==b[pos2])

            {

                vis[i]=;

                pos2++;

            }

        }

        if(pos1!=pos2)

            cout<<'-'<<endl;

        else

        {

            for(int i=;i<n;i++)

                cout<<vis[i];

            cout<<endl;

        }

    }

}