70.js

/** ------------------------------------------------------------------------------
 * 
 * 70. Climbing Stairs
 * Topics: Dynamic Programming
 * https://leetcode.com/problems/climbing-stairs/description/
 * 
 ------------------------------------------------------------------------------ */

/**
 * @param {number} n
 * @return {number}
 */
var climbStairs = function (n) {
  if (n <= 2) {
    return n
  }

  let prev2 = 1
  let prev1 = 2

  for (let i = 3; i <= n; i++) {
    let curr = prev1 + prev2
    prev2 = prev1
    prev1 = curr
  }

  return prev1
}

console.log(climbStairs(2))