69. Sqrt(x)

https://leetcode.com/problems/sqrtx/submissions/

1. Use Newton’s Method

//4 ms    5.9 MB
class Solution {
public:
    int mySqrt(int a) {
      double epsilon = 1e-2;
      double x = a;
      while (x * x - a > epsilon) {
          x = (x + a / x) / 2.0;
      }
      return x;
    }
};