Check if a integer is perfect square, i.e. its root is also a integer.

isPerfectSquare.cpp

bool isPerfectSquare(int x) {
  int sqr = Math.sqrt(x);
  
  return x == sqr * sqr;
}

bool isPerfectSquareFaster(int x) {
  if (x < 0) return false;
  int h = x & 0xf;
  if (h == 0 || h == 0x1 || h == 0x4 || h == 0x9) {
    return isPerfectSquare(x);
  }
  
  return false;
}