Problem: Climbing Stairs

Question

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

Solution

TODO

Code

class Solution {
    public int climbStairs(int n) {
        if(n==1) return 1;

        int first = 1;
        int second = 2;

        for(int i=2; i<n; i++) {
            int third = first + second;
            first = second;
            second = third;
        }

        return second;
    }
}

Performance