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

dp time o(n), space o(n);

class Solution {
    public int climbStairs(int n) {
     //输入的是n个台阶，一次要么一步，要么两步，问有多少不同的步数，那就建立一个维护当前不同步数的数组
        if(n <= 0)
            return 0;
        
        int[]dp = new int[n];
       
       if(n == 1)
           return 1;
        else if(n == 2)
            return 2;
        
         
        dp[1] = 1;
        dp[2] = 2;
        for(int i = 3; i < n;i++){
            dp[i] = dp[i-1]+dp[i-2];
        }
        
        return dp[n];
    }
}