70 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
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class Solution:
    def climbStairs(self, n: int) -> int:
        if n < 3:
            return n
        memo = [0] * n
        memo[0] = 1
        memo[1] = 2
        for i in range(2, n):
            memo[i] = memo[i-1] + memo[i-2]
        return memo[n-1]