Valid Perfect Square

class Solution {
    public boolean isPerfectSquare(int num) {
        int p = 1;
        int r = num;
        while (p <= r) {
            int x = p - (p - r) / 2;
            if (x * x == num) return true;
            else if (x * x < num) p = x + 1;
            else  r = x - 1;
        }
        return false;
    }
}