小白笔记---------------------------------leetcode(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.

Example 1:

Input: 2Output:  2Explanation:  There are two ways to climb to the top.1. 1 step + 1 step2. 2 steps

Example 2:

Input: 3Output:  3Explanation:  There are three ways to climb to the top.1. 1 step + 1 step + 1 step2. 1 step + 2 steps3. 2 steps + 1 step这很明显是个斐波那契数列，刚开始想用递归做，后来发现超时了，那就老老实实做斐波那契数列的推导就好了代码如下：
class Solution {    public int climbStairs(int n) {      if(n == 0 || n == 1|| n == 2){          return n;      }      int[] arr = new int[n+1];      arr[0] = 0;      arr[1] = 1;      arr[2] = 2;      for(int i = 3;i <= n;i++){          arr[i] = arr[i-1] + arr[i -2];      }      return arr[n];    }    }