LeetCode - 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
Output: true

Example 2:

Input: 14
Output: false


使用二分法，时间复杂度为O(n)

public boolean isPerfectSquare(int num) {//二分 my
        if(0==num||1==num){
            return true;
        }
        int left =1;
        int right = num;
        while(left<=right){
            int mid = left+ (right-left)/2;
            int y = num/mid;
            if(y==mid&&mid*mid ==num){
                return true;
            }
            else if(y>mid){
                left = mid+1;
            }
            else {
                right = mid-1;
            }
        }
        return false;
    }

 

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