qrt(x) II

Implement double sqrt(double x) and x >= 0.

Compute and return the square root of x.

 Notice

You do not care about the accuracy of the result, we will help you to output results.

Have you met this question in a real interview? 

Yes

Example

Given n = 2 return 1.41421356

计算时，需要注意小数的计算，当开方的数是小数时，将end的默认值定义为0；

java

public class Solution {
    /*
     * @param x: a double
     * @return: the square root of x
     */
    public double sqrt(double x) {
        // write your code here
        if (x < 0) {
            return -1;
        }
        double start = 0;
        double end = x;
        if (end < 1) {
            end = 1;
        }
        double mid = 0;
        double eps = 1e-12;
        while (end - start > eps) {
            mid = (end - start) / 2 + start;
            if (mid * mid > x) {
                end = mid;
            } else {
                start = mid;
            }
        }
        return start;
    }
}