【LeetCode】C# 70、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?

Note: Given n will be a positive integer.

爬阶问题。每次爬1或2阶，问有多少种爬法。
思路：每个阶数的方法数，等于他前两阶+2加上前一阶+1。抓着这个规律就好办了。

public class Solution {    public int ClimbStairs(int n) {        if(n<=2) return n;        int[] count = new int[3];        count[1]=1;        count[2]=2;        for(int i=3;i<=n;i++){            count[i%3] = count[(i+1)%3]+count[(i-1)%3];        }        return count[n%3];    }}