bool canISaveMidMice(int mid, vector<int>a, int n)
{ 
//  0 1 2 3 4 5 6   7 8  9 10  
  //1 2 3 4 5 6 7 | 8 9 10 11
  //n = 11
  int mouse =  0, sum = 0, ind = a.size() - mid ;//11 - 4 = 6 
   while(ind < a.size())
    {
      if(mouse >= a[ind])return false;
      sum += (n - a[ind]);
      mouse += (n - a[ind]);
      ind++;
    }

    return true;
}
void solve()
{
  int n, k;
  cin>>n>>k;

  _vi v(k);
  for(auto &it : v)cin>>it;
    sort(_a(v));
    
  int l = 0, h = k;
int ans = 0;
  while(l <= h)
  {
    int mid = l - ((l - h)/2);
    if(canISaveMidMice(mid, v, n) == false)
    {
      h = mid - 1;
    }
    else
    {
      ans = max(ans, mid);
      // debug(ans);
      l = mid + 1;    
    } 
  }

cout<<ans<<endl;

   return;
  
}
[Problem Link](https://mirror.codeforces.com/problemset/problem/1593/C)