climbStairs.js

/*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
 

Constraints:

1 <= n <= 45
*/

/**
 * @param {number} n
 * @return {number}
 */
var climbStairs = function (n) {
  if (n < 3) {
    return n;
  }
  let firstNum = 1;
  let secondNum = 2;
  for (let i = 3; i <= n; i++) {
    let result = firstNum + secondNum;
    firstNum = secondNum;
    secondNum = result;
  }

  return secondNum;
};

console.log(climbStairs(4));
/*
1. 1 шаг + 1 шаг + 1 шаг + 1 шаг 
2. 2 шага + 2 шага
3. 2 шага + 1 шаг + 1 шаг
4. 1 шаг + 2 шага + 1 шаг
5. 1 шаг + 1 шаг + 2 шага

*/