70. Climbing Stairs

LeetCode problem

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

First accepted

Idea:

Tried to calculate by hand. There is a sequence Fibonacci here

class Solution:
    def climbStairs(self, n: int) -> int:
        if n == 1:
            return 1
        if n == 2:
            return 2
        
        prev1 = 1
        prev2 = 2
        current = 2
        while n > 2:
            current = prev1 + prev2
            prev1 = prev2
            prev2 = current
            n -= 1
        return current