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

 

class Solution {
public:
    int climbStairs(int n) {
        int a[n+2],i;
        a[1]=1;
        a[2]=2;
        for(i=3;i<=n;i++){
            a[i]=a[i-1]+a[i-2];
        }
        return a[n];
    }
};