70. Climbing Stairs（js）

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

Example 2:

Input: 3
Output: 3
Explanation: There are three ways to climb to the top.
1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step

题意：给定梯子阶层数，每次只能爬一阶或者两阶，求出所有可能爬完楼梯

代码如下：

/**
 * @param {number} n
 * @return {number}
 */
var climbStairs = function(n) {
    if(n==0 || n==1 || n==2) return n;
    var arr=[];
     arr[0]=1;
     arr[1]=2;
    for(var i=2 ; i< n;i++){
        arr[i]=arr[i-1]+arr[i-2];
    }
    
    return arr[n-1];
};