LeetCode 70. Climbing Stairs

题目

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?

Example 1:

1
2
3
4
5
Input: 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps

Example 2:

1
2
3
4
5
6
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

Constraints:

  • 1 <= n <= 45

思路

Solution.

代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
class Solution(object):
def climbStairs(self, n):
"""
:type n: int
:rtype: int
"""
if n == 1:
return 1
first = 1
second = 2
for i in range(3, n+1):
third = first + second
first = second
second = third
return second