70. Climbing Stairs

You are climbing a stair case. It takesnsteps 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:Givennwill 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

Code

class Solution {
public:
    int climbStairs(int n) {
        if( n < 0) return 0;
        int d[n + 1]; fill_n(d,n+1,1);
        cout<<d[0]<<endl;
        for(int i = 2; i <= n; i++){
            d[i] = d[i-1] + d[i-2];
        }

        return d[n];
    }
};