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
SOLUTION:
class Solution:
    def climbStairs(self, n: int) -> int:
        a = 1
        b = 2
        if n == 1:
            return a
        if n == 2:
            return b
        for _ in range(n - 2):
            a, b = b, a + b
        return b

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