2.1.18 Climbing Stairs

Link: https://oj.leetcode.com/problems/climbing-stairs/

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?

我的思路：Fibonacci 數列。一次過。

Time: O(n) 

Note: Return f2, not fn. Since when n = 1, fn = 0, f1= 1.

public class Solution {
    public int climbStairs(int n) {
        int f1 = 1;
        int f2 = 1;
        int fn = 0;
        for(int i = 2; i <= n; i++){
            fn = f1+f2;
            f1= f2;
            f2 = fn;
        }
        return f2;
    }
}

TODO: Math

http://blog.csdn.net/linhuanmars/article/details/23976963