Method myPow

src/com/blankj/medium/_0050/Solution.java:12–15

(double x, int n)

 */
public class Solution {
    public double myPow(double x, int n) {
        if (n < 0) return helper(1 / x, -n);
        return helper(x, n);
    }

    private double helper(double x, int n) {
        if (n == 0) return 1;