You are climbing a stair case. It takes n steps to reach to the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? http://leetcode.com/onlinejudge#question_70

leetcode_climbing_stairs.cpp

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