[LeetCode]70. Climbing Stairs(Easy)

Sherlock Chiou

·

Follow

1 min read

·

Mar 17, 2021

--

Listen

Share

Description:

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

Solution 1:

Time complexity O(N²). Find the combination of each solution.

Solution 2:

Time complexity O(N). Dynamic Programming. The n stair can be reached from either n-1 stair with 1 step, or n-2 stair with 2 step. So the total possible steps would be equivalent to solution[n-1] plus soultion[n-2]. The base cases: one stair for one step, two stair for two possible steps.