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Author: hogan-tech

0104-maximum-depth-of-binary-tree/0104-maximum-depth-of-binary-tree.py

@@ -0,0 +1,67 @@
+# time complexity: O(n)
+# space complexity: O(logn)
+from typing import Optional
+
+
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        def longestPath(node: Optional[TreeNode]):
+            if not node:
+                return 0
+            leftPath = longestPath(node.left)
+            rightPath = longestPath(node.right)
+            return max(leftPath, rightPath)+1
+        return longestPath(root)
+
+
+# time complexity: O(n)
+# space complexity: O(n)
+class Solution:
+    def __init__(self):
+        self.nextItem = []
+        self.maxDepth = 0
+
+    def nextMaxDepth(self):
+        if not self.nextItem:
+            return self.maxDepth
+        nextNode, nextLvl = self.nextItem.pop(0)
+        nextLvl += 1
+        self.maxDepth = max(self.maxDepth, nextLvl)
+        if nextNode.left:
+            self.nextItem.append((nextNode.left, nextLvl))
+        if nextNode.right:
+            self.nextItem.append((nextNode.right, nextLvl))
+        return self.nextMaxDepth()
+
+    def maxDepth(self, root):
+        if not root:
+            return 0
+        self.nextItem = []
+        self.maxDepth = 0
+        self.nextItem.append((root, 0))
+        return self.nextMaxDepth()
+
+# time complexity: O(n)
+# space complexity: O(n)
+class Solution:
+    def maxDepth(self, root: TreeNode) -> int:
+        stack = []
+        if root is not None:
+            stack.append((1, root))
+
+        depth = 0
+        while stack != []:
+            currDepth, root = stack.pop()
+            if root is not None:
+                depth = max(depth, currDepth)
+                stack.append((currDepth + 1, root.left))
+                stack.append((currDepth + 1, root.right))
+
+        return depth