Pow(x, n)

Implement pow(x, n).

public class Solution {
    public double pow(double x, int n) {
        //判断x是不是0
        if(Math.abs(x-0)<0.0000001)
            return 1;
        //指数为负数
        if(n<0){
            return 1/p(x,-((long)n));
        }
        if(n==0)
            return 1;
        return p(x,n);

    }

    public double p(double x,long n){
        if(n==0)
            return 1;
        if(n==1)
            return x;
        if(n%2==0){
            double r=p(x,n/2);
            return r*r;
        }
        double r=p(x,(n-1)/2);
        return r*r*x;
    }
}