69. x 的平方根

输入: 4
输出: 2

输入: 8
输出: 2
说明: 8 的平方根是 2.82842..., 
     由于返回类型是整数，小数部分将被舍去。

class Solution {
    public int mySqrt(int x) {
        if (x == 0) {
            return 0;
        }
        int start = 1;
        int end = x;
        while (start + 1 < end) {
            int mid = start + (end - start) / 2;
            int val = x / mid;
            if (val == mid) return mid;
            else if (val > mid) {
                start = mid;
            } else {
                end = mid;
            }
        }
        return start;
    }
}

class Solution {
    public int mySqrt(int x) {
        long r = x;
        while (r * r > x) {
            r = (r + x / r) / 2;
        }
        return (int) r;
    }
}