70. 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

My solution

/**
 * @param {number} n
 * @return {number}
 */
var climbStairs = function(n) {
  if (n<=3) return n
  let [pre, cur] = [1,2]
  while(--n>1) {
    [pre, cur] = [cur, cur+pre]
  }
  return cur
};