完全平方数

给出一个正整数 num,写一个函数，要求当这个当num为完全平方数时函数返回True，否则返回False

样例

样例1:

输入: num = 16
输出: True
解释:
sqrt(16) = 4

样例2:

输入: num = 15
输出: False
解释:
sqrt(15) = 3.87

注意事项

不要用诸如sqrt的库函数

class Solution {
public:
    /**
     * @param num: a positive integer
     * @return: if num is a perfect square else False
     */
    bool isPerfectSquare(int x) {
        // write your code here
        long left = 1;
        long right = x;
        while(left <= right)
        {
            long mid = (left + right) / 2;
            long tmp = x / mid;
            if(tmp == mid)
                return (mid*mid == x);
            else if(tmp > mid)
            {
                left = mid + 1;
            }
            else if(tmp < mid)
            {
                right = mid - 1;
            }
        }
        return (right*right == x);
    
    }
};