50. Pow(x, n)

输入: 2.00000, 10
输出: 1024.00000

输入: 2.10000, 3
输出: 9.26100

输入: 2.00000, -2
输出: 0.25000
解释: 2-2 = 1/22 = 1/4 = 0.25

class Solution {
    public double myPow(double x, int n) {
        if (n == 0) {
            return 1;
        }
        if (n == 1) {
            return x;
        }
        int t = n / 2;
        if (n < 0) {
            t = -t;
            x = 1 / x;
        }
        double res = myPow(x, t);
        if (n % 2 == 0) {
            return res * res;
        }
        return res * res * x;
    }
}