Leetcode 367. Valid Perfect Square

367. Valid Perfect Square

• Total Accepted: 11219
• Total Submissions: 30842
• Difficulty: Medium

 

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

 

思路：二分法。

 

代码：

class Solution {
public:
    bool isPerfectSquare(int num) {
        int left=1,right=num-1;
        while(left<=right){
            long long mid=left+(right-left)/2;
            if(mid*mid<num){
                left=mid+1;
            }
            else{
                right=mid-1;
            }
        }
        return left*left==num;
    }
};