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?

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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
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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
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Constraints:

1 <= n <= 45

Approach

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class Solution:
    def climbStairs(self, n: int) -> int:
        if n == 1:
            return 1
        elif n == 2:
            return 2
        else:
            return self.climbStairs(n - 1) + self.climbStairs(n - 2)
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class Solution:
    def climbStairs(self, n: int) -> int:
        dp = [0] * (n+1)
        dp[1] = 1
        dp[0] = 1
        for i in range(2,n+1):
            dp[i] = dp[i-1] + dp[i-2]
        return dp[n]