答案

public class Solution {
    public double pow(double x, int n) {
        boolean positive=true;
        long N=n;
        if(N<0){
            N=-N;
            positive=false;
        }
        double result=1;
        double current=x;
        long p=1;
        while(N>0)
        {
            if((N&p)>0)
            {
                N-=p;
                result*=current;
            }
            current*=current;
            p=p<<1;
        }
        if(!positive)
        {
            result=1/result;
        }
        return result;
    }
}