[SAM] Week 3 solutions.

climbing-stairs/samthekorean.py

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+# Time complexity : O(n)
+# Space complexity : O(1)
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        a = 1
+        b = 2
+        result = 0
+        if n == 1:
+            return a
+
+        if n == 2:
+            return b
+
+        for i in range(3, n + 1):
+            result = a + b
+            a, b = b, result
+
+        return result

maximum-depth-of-binary-tree/samthekorean.py

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+# Time complexity : O(n)
+# Space complexity : O(n)
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        if not root:
+            return 0
+
+        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))

meeting-rooms/samthekorean.py

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+# Time complexity : O(nlog(n))
+# Space complexity : O(1)
+class Solution:
+    def canAttendMeetings(self, intervals: List[List[int]]) -> bool:
+        intervals.sort()
+        for i in range(len(intervals) - 1):
+            if intervals[i][1] > intervals[i + 1][0]:
+                return False
+        return True

same-tree/samthekorean.py

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+# Time complexity : O(n)
+# Space complexity : O(n)
+class Solution:
+    def isSameTree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
+        if not p and not q:
+            return True
+
+        if not p and q:
+            return False
+
+        if p and not q:
+            return False
+
+        if p.val != q.val:
+            return False
+
+        return self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)

subtree-of-another-tree/samthekorean.py

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+# Time complexity: O(n*m)
+# Space complexity: O(r + s) isSubtree() method is internally calling isSameTree() so the total depth of the stack is sum of isSubtree() call stacks and isSameTree()'s call stacks.
+class Solution:
+    def isSubtree(self, p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
+        if not q:
+            return True
+
+        if not p:
+            return False
+
+        if self.isSameTree(p, q):
+            return True
+
+        return self.isSubtree(p.left, q) or self.isSubtree(p.right, q)
+
+    def isSameTree(self, p, q) -> bool:
+        if not p and not q:
+            return True
+
+        if not p and q:
+            return False
+
+        if p and not q:
+            return False
+
+        if p.val != q.val:
+            return False
+
+        return self.isSameTree(p.left, q.left) and self.isSameTree(p.right, q.right)