ValidPerfectSquare.java

class ValidPerfectSquare {
    public boolean isPerfectSquare(int num) {
        if (num < 2) {
            return true;
        }
        long left = 1l;
        long right = num;
        long mid, product;
        while (left <= right) {
            mid = left + (right - left) / 2;
            product = mid * mid;
            if (product == num) {
                return true;
            } else if (product < num) {
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        return false;
    }
}