(Leet Code c++)Valid Perfect Square

367. Valid Perfect Square

 

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

 

Constraints:

• 1 <= num <= 2^31 - 1

이분 탐색을 통한 문제 풀이.

 

class Solution {
public:
    bool isPerfectSquare(int num) {
        int front = 1;
        int back = num;
        
        while(front <= back){
            int mid = front + (back - front) / 2;
            
            if(mid == (double)num / (double)mid){
                return true;
            }
            else if(num / mid > mid){
                front = mid + 1;
            }
            else{
                back = mid - 1;
            }
        }
        
        return false;
    }
};