9.1 A child is running up a staircase with n steps, and can hop either 1 step, 2 steps, or 3 steps at a time. Implement a method to count how many possible ways the child can run up the stairs.
LeetCode上的原题，请参见我之前的博客Climbing Stairs 爬梯子问题。
class Solution { public: int countWays(int n) { vector<int> res(n + 1, 1); for (int i = 2; i <= n; ++i) { res[i] = res[i - 1] + res[i - 2]; } return res.back(); } };
[CareerCup] 9.1 Climbing Staircase 爬楼梯
原文：http://www.cnblogs.com/grandyang/p/4815094.html