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

想法：完全平方数是等差数列相加。

class Solution {
public:
    bool isPerfectSquare(int num) {
        ;
         ){
            num = num - x;
            x = x + ;
        }
        ;
    }
};