class Solution {
public:
    int jumpFloorII(int number) {
        int res[25] = {0};
        res[0] = 1;
        res[1] = 1;
        for (int i = 2; i <= number; ++i) {
            res[i] = 2 * res[i-1];
        }
        return res[number];
    }
};