[LC] 367. Valid Perfect Square

Posted 2020-11-23 xuanlu

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

Note: Do not use any built-in library function such as sqrt.

Example 1:

Input: 16
Output: true

Example 2:

Input: 14
Output: false

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) {
                left = (int)mid + 1;
            } else {
                right = (int)mid - 1;
            }
        }
        return false;
    }
}