Valid Perfect Square

https://leetcode.com/problems/valid-perfect-square/description/

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

Thoughts

和sqrt(x)同理. 只是这次无论是二分还是牛顿法得到的最终结果不是直接返回, 而是与自身相乘看是否与num相等.

Code

class Solution {
    public boolean isPerfectSquare(int num) {
        long r = num;
        while (r * r > num) {
            r = (r + num / r) / 2;
        }

        return r * r == num;
    }
}

Analysis

时间复杂度未知.