70. Climbing Stairs

public class Solution {    public int climbStairs(int n) {        if(n<=0) {            return 0;        }        if(n==1 || n == 2) {            return n;        }        int[] nums = new int[n+1];        nums[1] = 1;        nums[2] = 2;        for(int i = 3; i<=n;i++) {            nums[i] = nums[i-1]+nums[i-2];        }        return nums[n];    }}