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 数列。一次过。

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