http://www.leetcode.com/onlinejudge http://www.leetcode.com/onlinejudge

leetcode_climbing_stairs.cpp

class Solution {
public:
    int climbStairs(int n) {
        int f[3] = {1, 0, 0};
        int cur = 0;
        for (int i = 1; i <= n; ++i) {
            cur = i % 3;
            f[cur] = f[0] + f[1] + f[2] - f[cur];
        }
        return f[cur];
    }
};