[lintcode]141. x的平方根

链接：https://www.lintcode.com/zh-cn/problem/sqrtx/

实现 int sqrt(int x) 函数，计算并返回 x 的平方根。

您在真实的面试中是否遇到过这个题？  

Yes

样例

sqrt(3) = 1

sqrt(4) = 2

sqrt(5) = 2

sqrt(10) = 3

class Solution {
public:
    /**
     * @param x: An integer
     * @return: The sqrt of x
     */
    int sqrt(int x) {
        // write your code here
        int low = 0, high = x;
        while(low <= high) {
            int mid = low + (high - low)/2;
            long long square = (long long)mid * (long long)mid;
            long long square1 = (long long)(mid + 1) * (long long)(mid + 1);
            long long square2 = (long long)(mid - 1) * (long long)(mid - 1);

            if(square == x) return mid;
            if(square < x && square1 > x) return mid;
            if(square > x && square2 < x) return mid - 1;
            if(square < x) low = mid + 1;
            else high = mid - 1;
        }
        return -1;

    }
};