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070. Climbing Stairs.py
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070. Climbing Stairs.py
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70. Climbing Stairs
Easy
1613/62
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
-----
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# Standard DP
class Solution:
def climbStairs(self, n):
if n <= 2: return n
dp = [0] * (n+1)
dp[0] = 0
dp[1] = 1
dp[2] = 2
for i in range(3,n+1):
dp[i] = dp[i-1] + dp[i-2]
return dp[-1]
# O(1) memory
class Solution:
def climbStairs(self, n):
if n <= 2: return n
a = 1
b = 2
for i in range(3,n+1):
c = a + b
a = b
b = c
return c
class Solution:
def climbStairs(self, n):
"""
:type n: int
:rtype: int
"""
if n == 0: return 0
if n == 1: return 1
if n == 2: return 2
else: return self.climbStairs(n-1) + self.climbStairs(n-2)