367. Valid Perfect Square

Given a positive integer num, write a function which returns True if num is a perfect square else False.

题目含义：判断一个数能否被开方

    public boolean isPerfectSquare(int num) {
        for (int i = 1; i <= num / i; ++i) {
            if (i * i == num) return true;
        }
        return false;        
    }