367. Valid Perfect Square

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
Returns: True

Example 2:

Input: 14
Returns: False

class Solution {
public:
    bool isPerfectSquare(int num) {
       if(num == 0 || num == 1) return true;
       
        long a = num/2;
        long square = a*a;
        while(square > num)
        {
                a = a/2;
                square = a*a;
        }
        
        for(long i = a;i<=a*2;i++)
        {
            if(i*i == num) return true;
        }
        
        return false;
    }
};