Create Climbing Stairs - Leetcode 70.py

Author: gahogg

Climbing Stairs - Leetcode 70.py

@@ -0,0 +1,67 @@
+# Recursive Solution
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        if n == 1:
+            return 1
+        if n == 2:
+            return 2
+        
+        return self.climbStairs(n-2) + self.climbStairs(n-1)
+        # Time: O(2^n)
+        # Space: O(n)
+
+
+# Top Down Memoization
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        memo = {1:1, 2:2}
+        def f(n):
+            if n in memo:
+                return memo[n]
+            else:
+                memo[n] = f(n-2) + f(n-1)
+                return memo[n]
+        
+        return f(n)
+        # Time: O(n)
+        # Space: O(n)
+
+
+# Bottom Up Tabulation
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        if n == 1:
+            return 1
+        if n == 2:
+            return 2
+        
+        dp = [0] * n
+        dp[0] = 1
+        dp[1] = 2
+
+        for i in range(2, n):
+            dp[i] = dp[i-2] + dp[i-1]
+        
+        return dp[n-1]
+        # Time: O(n)
+        # Space: O(n)
+
+
+# Bottom up Constant Space
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        if n == 1:
+            return 1
+        if n == 2:
+            return 2
+        
+        two_back = 1
+        one_back = 2
+        for i in range(2, n):
+            next_num = two_back + one_back
+            two_back = one_back
+            one_back = next_num
+        
+        return one_back
+        # Time: O(n)
+        # Space: O(1)