70. Climbing Stairs

catepk·2021년 8월 28일
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70. Climbing Stairs

문제

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

풀이

-----memoization-----

class Solution:
    dp = collections.defaultdict(int)
    def climbStairs(self, n: int) -> int:
        if n <= 2:
            return n
        if self.dp[n]:
            return self.dp[n]
        self.dp[n] = self.climbStairs(n - 1) + self.climbStairs(n - 2)
        return self.dp[n]
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