题目链接：https://leetcode-cn.com/problems/valid-perfect-square/
题目如下：

class Solution {
public:
    bool isPerfectSquare(int num) {
        int low=1,high=num,mid;

        while(low<high){
            mid=(low+1ll+high)>>1;

            if(mid<=num/mid) low=mid;
            else high=mid-1;

        }

        if(high*high==num) return true;
        else return false;
    }
};