Climbing Stairs

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?

Given n will be a positive integer.

Example:

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

Write your solution:

function main (n) {
    return;
}

function main (n) {
    return;
}

Test Case 1

Input: 2
Output: 2

Test Case 2

Input: 3
Output: 3

Test Case 3

Input: 4
Output: 5

Test Case 4

Input: 13
Output: 377

Solution

Complexity:

function climbStairs(n) {
    let a = 0,
        b = 1;

    for (let i = 0; i < n; i++) {
        [a, b] = [b, a + b];
    }

    return b;
}