leetcode50. Pow(x, n)

class Solution {
public:
    double myPow(double x, int n) {
        double ans=1.0;
        if(x==0)return 0.0;
        long  b=n;
        if(b<0){
            x=1/x;
            b=-b;
        }
        while(b){
                if(b&1)ans*=x;
                x*=x;
                b>>=1;
            }
        
        return ans;
    }
};