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。

非递归：

class Solution {
public:
    int jumpFloorII(int number) {
        
        if (number == 0)
        {
            return 0;
        }
        else if (number == 1)
        {
            return 1;
        }
        vector<int> result;
        result.push_back(0);
        result.push_back(1);
        int tmp = 1;
        for (int i = 2; i <= number; i++)
        {
            result.push_back(2*result[i-1]);
        }
        
        return result[number];
        
        
        /*
        vector<int> dp;
        if (number == 0)
        {
            return 0;
        }
        else if (number == 1)
        {
            return 1;
        }
        else if (number == 2)
        {
            return 2;
        }
        dp.push_back(1);
        dp.push_back(1);
        dp.push_back(2);
        int k = 3;
        while (k <= number)
        {
            int temp = 0;
            int i = 0;
            while (i < k)
            {
                temp += dp[i];
                i++;
            }
            dp.push_back(temp);
            k++;
        }
        return dp[number];
        */
    }
    
};

递归：

class Solution {
public:
    int jumpFloorII(int number) {
        
        if (number == 0)
        {
            return 0;
        }
        else if (number == 1)
        {
            return 1;
        }
        else
        {
            return 2 * jumpFloorII(number - 1);
        }
    }
    
};