Pow(x, n)

public class  {
    public double myPow(double x, int n) {
        if(n==0) return 1;
        if(x==1) return 1;
        if(x==-1) return (n%2)==0?1:-1;
        if(n == Integer.MIN_VALUE) return 0;
        if(n<0) {
            n = -n;
            x = 1/x;
        }
        
        
        //非递归、位运算
        double res = 1;
        while(n > 0) {
            if((n&1)==1) res *= x;
            x *= x;
            n >>= 1;
        }
        return res;
        
    }
}