Climbing Stairs

Author: anantkaushik

70-climbing-stairs.py

@@ -22,11 +22,36 @@
 2. 1 step + 2 steps
 3. 2 steps + 1 step
 """
-class Solution(object):
- def climbStairs(self, n):
- if n == 1:
- return 1
- a,b = 1,2
- for _ in range(2,n):
- a,b = b, a+b
- return b
+class Solution:
+ def climbStairs(self, n: int) -> int:
+ if n <= 2:
+ return n
+ 
+ second_last_stair, last_stair = 1, 2 
+ 
+ for _ in range(3, n+1):
+ second_last_stair, last_stair = last_stair, last_stair + second_last_stair
+ 
+ return last_stair
+
+
+class Solution1:
+ def climbStairs(self, n: int) -> int:
+ return self.helper(n, {})
+ 
+ def helper(self, n, memo):
+ if n <= 2:
+ return n
+ 
+ if n not in memo:
+ memo[n] = self.helper(n-1, memo) + self.helper(n-2, memo)
+ 
+ return memo[n]
+
+
+# TLE
+class Solution2:
+ def climbStairs(self, n: int) -> int:
+ if n <= 2:
+ return n
+ return self.climbStairs(n-1) + self.climbStairs(n-2)