#include <bits/stdc++.h>
#define faster() ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int uint;
void solve()
{
int key,max,k,d=0,i=0;
string s;
cin >> k;
cin >> s;
while (d<k && i<s.size())
{
max=-1;
for (int j=s.size()-1; j>i; j--)
{
if (s[j]-48>max)
{
max=s[j]-48;
key=j;
}
}
if (max>s[i]-48)
{
swap(s[i],s[key]);
d++;
}
i++;
}
cout << s << endl;
}
int main()
{
faster();
int t;
cin >> t;
while (t--)
{
solve();
}
return 0;
}
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