#include <bits/stdc++.h>   using namespace std;   int main() {     long long t, a, b;     string s;     scanf( %lld , &t);     vector<int> v;     while (t--) {       v.clear();       scanf( %lld%lld , &a, &b);       cin >> s;       for (int i = 0; i < s.length(); i++) {         if (s[i] ==  0 ) v.push_back(i);       }       int w = -1;       for (int i = 0; i < v.size(); i++) {         if (b > v[i] - w - 1) {           b = b - (v[i] - w - 1);           v[i] = w + 1;           w = v[i];         } else {           v[i] = v[i] - b;           break;         }       }       v.push_back(1000025);       int k = 0;       for (int i = 0; i < a; i++) {         if (i == v[k]) {           cout <<  0 ;           k++;         } else {           cout <<  1 ;         }       }       cout << endl;     }   }   