70. Climbing Stairs

문제

You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

Note: Given n will be a positive integer.

Example 1:

Input: 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps

Example 2:

Input: 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

풀이

중복 계산을 제거하도록 memoization을 사용합니다.

class Solution:
    cache = {}
    def climbStairs(self, n: int) -> int:
        if n < 3:
            return n
        else :
            return self._climbStairs(n-1) + self._climbStairs(n-2)

    def _climbStairs(self, n: int):
        if n not in self.cache.keys() :
            self.cache[n] = self.climbStairs(n)
        return self.cache[n]