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:
Input: 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps
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
Solution:
class Solution1: """ 递归做法 """ def climbStairs(self, n): """ :type n: int :rtype: int """ if n == 1: return 1 if n == 2: return 2 return self.climbStairs(n-1) + self.climbStairs(n-2) class Solution2: """ 非递归做法 """ def climbStairs(self, n): """ :type n: int :rtype: int """ pre_1_step = 1 pre_2_step = 0 count = 1 for i in range(1, n+1): count = pre_1_step + pre_2_step pre_2_step = pre_1_step pre_1_step = count return count class Solution: """ 非递归做法,比上一个方法快 """ def climbStairs(self, n): """ :type n: int :rtype: int """ F = [0, 1] count = 1 for i in range(n): count = F[0] + F[1] F[0] = F[1] F[1] = count return count
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