// Q: Find minimum and maximum number made out of all 9 digits which is a perfect square


bool isPerfectSquare(const char *s) {
  int num;
  {
    stringstream ss(s);
    if( !(ss >> num) ) return false;
    static const bool possible_sq[] = {true, true, false, false, true, true, true, false, false, true};
    if( !possible_sq[num % 10] ) return false;
  }
  const int c = num;

  int res = 0;
  int bit = 1 << 30;

  while (bit > num) bit >>= 2;

  while (bit != 0) {
    if (num >= res + bit) {
      num -= res + bit;
      res = (res >> 1) + bit;
    } else res >>= 1;
    bit >>= 2;
  }
  return (res * res == c);
}

int main() {
  char num[] = "123456789";
  char *const f = &num[0];
  char *const t = &num[9];
  bool found = false;
  do {
    if( isPerfectSquare(num) ) {
      cout << "Smallest is: "  << num << endl;
      found = true;
      break;
    }
  } while( next_permutation(f, t) );

  if( !found ) {
    cout << "None found" << endl;
    return 0;
  }

  sort( f, t, std::greater<char>() );
  do {
    if( isPerfectSquare(num) ) {
      cout << "Largest is: "  << num << endl;
      break;
    }
  } while( next_permutation( f, t, std::greater<char>() ) );
}

Smallest is: 139854276
Largest is: 923187456