17.climbing-stairs.js

// // https://leetcode.com/problems/climbing-stairs/
// 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}
 */

 const hashMap = {};

 var climbStairs = function(n) {
     
     return helper(n);
 };
 
 function helper(n) {    
     if (hashMap[n]) {
         return hashMap[n];
     }
     
     if (n === 1) return 1;
     if (n === 2) return 2;
     
     let result = helper(n - 1) + helper(n - 2);
     hashMap[n] = result;
     return result;
 }