367. Valid Perfect Square

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LeetCode

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Problem

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

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

Example 1:

Input: num = 16
Output: true

Example 2:

Input: num = 14
Output: false

Code

class Solution {
    public boolean isPerfectSquare(int num) {
        long left = 1;
        long right = num / 2;

        while(left + 1 < right) {
            long mid = (left + right) / 2;
            if(mid * mid == num) return true;

            if(mid * mid > num) {
                right = mid;
            } else {
                left = mid;
            }
        }

        if(left * left == num) return true;
        if(right * right == num) return true;

        return false;
    }
}