leetcode :Binary Search：Valid Perfect Square(367)

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

---

class Solution {public:    bool isPerfectSquare(int num) {        if (num == 1) return true;        long x = num / 2, t = x * x;        while (t > num) {            x /= 2;            t = x * x;        }        for (int i = x; i <= 2 * x; ++i) {            if (i * i == num) return true;        }        return false;    }};