I was trying to solve this problem in a recursive way and store results that are computed in a Hashtable. But it has compile error saying cannot find class Hashtable. But it works in eclipse.

```
public class Solution {
Hashtable<Integer,Integer> results = new Hashtable<Integer,Integer>();
public int climbStairs(int n) {
if(n<0)
return 0;
if(n<=1){
results.put(n,1);
return 1;
}
Integer tmp=results.get(n);
if( tmp== null){
tmp = climbStairs(n-1)+climbStairs(n-2);
results.put(n,tmp);
}
return tmp;
}
}
```