climbStairs.js

// 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?

// 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

/**
 * @param {number} n
 * @return {number}
 */
 
var climbStairs = function(n) {
    let first = 1;
    let second = 2;
    
    if (n === 1) {
        return first;
    }
    
    for (let i = 2; i < n; i++) {
        let temp = first + second;
        first = second;
        second = temp;
    }
    return second;
};