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?

这道题可以用 recursive或者DP做，但是recursive 的效率太低了。

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