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Practice Problem

Climbing Stairs

Difficulty: Easy

Given n steps, find the number of distinct ways to climb to the top when you can take 1 or 2 steps at a time.

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?

Examples

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

Example 3:

Input: n = 5
Output: 8
Explanation: The 8 ways are:
1. 1+1+1+1+1
2. 1+1+1+2
3. 1+1+2+1
4. 1+2+1+1
5. 2+1+1+1
6. 1+2+2
7. 2+1+2
8. 2+2+1

Constraints

  • 1 <= n <= 45

Expected Complexity

  • Time: O(n)
  • Space: O(1)
EASY
Dynamic Programming
Tabulation
Memoization
Fibonacci
Beginner

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Solution

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