Valid Perfect Square

public class Solution {
    public boolean isPerfectSquare(int num) {
        if(num <= 0) return false;
        int left = 0, right = num;
        while(left <= right) {
            long mid = left + (right-left)/2;
            if(mid * mid == num) {
                return true;
            } else if(mid * mid > num) {
                right = (int)mid - 1;
            } else {
                left = (int)mid + 1;
            }
        }
        return false;
    }
}