题解 | #跳台阶扩展问题#

第一步先写出递推式dp[n] = dp[n - 1] + dp[n - 2] + ... + dp[1]，然后观察，由于dp[n - 1] = dp[n - 2] + ... + dp[1]，化简后得到dp[n] = 2 * dp[n - 1]。

class Solution {
public:
    int jumpFloorII(int number) {
        if (number == 1) return 1;
        int res = 1;
        for (int i = 2; i <= number; i++) {
            res *= 2;
        }
        return res;
    }
};