public double myPow(double x, int n) {

        if (n==0) return 1.0;

        else if (n>0)

        {

            double half = (double) myPow(x,n/2);

            if (n%2==0) return half*half;

            else return half*half*x;

        }

        else {

            if (n==Integer.MIN_VALUE)

            {

                double half = myPow(x,n/2);

                return (half*half);

            }

            n=-n;

            double half = myPow(x,n/2);

            if (n%2==0) return 1.0/(half*half);

            else return 1.0/(half*half*x);

        }

    }

public int mySqrt(int x) {

        /*

        二分法一个一个寻找答案

         */

        if (x==0) return 0;

        long sta = 1;

        long end = x/2+1;

        while (sta<end)

        {

            long mid  = (sta+end)/2;

            long cur = mid*mid;

            if (cur==x) return (int)mid;

            if (cur>x) end = mid-1;

            else sta = mid+1;

        }

        return (int)sta;

    }