Digo plays with Numbers

#include<iostream>
#include<string>
using namespace std;
int t, n, k;
string s;
bool check()
{
    bool check0 = false;
    bool check1 = false;
    for (int i = 0; i < n; i++)
    {
        if (s[i] == '0') check0 = true;
        if (s[i] == '1') check1 = true;
        if (check0 &&check1) return true;
    }
    return false;
}
void slove(char bit)
{
    if (!check())
    {
        int index = 0;
        while (s[index] == 'a')
        {
            index++;
        }
        s[index] = 'a';
    }
    else
    {
        for (int i = 0; i < n; i++)
        {
            if (s[i] == bit) { s[i] = 'a'; break; }
        }
    }
}
void print()
{
    for (int i = 0; i < n; i++)
    {
        if (s[i] != 'a') cout << s[i];
    }
    cout << endl;
}
int main()
{
    freopen("input.txt", "r", stdin);
    cin >> t;
    for (int tc = 0; tc < t; tc++)
    {
        cin >> n >> k >> s;
        int N = n, cnt = 0;
        while (N != k)
        {
            if (cnt % 2 == 0) slove('1');
            else slove('0');
            cnt++; N--;
        }
        print();
    }
    return 0;
}