Climbing Stairs

You are climbing a staircase. It takes n steps to reach the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? 

Example 1:

Input: n = 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps

Example 2:

Input: n = 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

Solutions 

public class Solution {

public int climbStairs(int n) {

if (n == 1) {

return 1;

}

int first = 1;

int second = 2;

for (int i = 3; i <= n; i++) {

int third = first + second;

first = second;

second = third;

}

return second;

}

}