9、变态跳台阶

一只青蛙一次可以跳上1级台阶，也可以跳上2级……它也可以跳上n级。求该青蛙跳上一个n级的台阶总共有多少种跳法。

===========Python=========

# -*- coding:utf-8 -*-
class Solution:
    def jumpFloorII(self, number):
        # write code here
        return 2 ** (number - 1)

=============Java===========

public class Solution {
    public int JumpFloorII(int target) {
        int[] dp = new int[target];
        for (int i = 0; i < target; i++) {
            dp[i] = 1;
        }
        for (int i = 1; i < target; i++) {
            for (int j = 0; j < i; j++) {
                dp[i] += dp[j];
            }
        }
        return dp[target-1];
    }
}