maximum-depth-of-bt py3

0104_maximum-depth-of-binary-tree/README.md

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+Given the `root` of a binary tree, return _its maximum depth_.
+
+A binary tree's **maximum depth** is the number of nodes along the longest path from the root node down to the farthest leaf node.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/11/26/tmp-tree.jpg)
+
+    Input: root = [3,9,20,null,null,15,7]
+    Output: 3
+    
+
+**Example 2:**
+
+    Input: root = [1,null,2]
+    Output: 2
+    
+
+**Constraints:**
+
+*   The number of nodes in the tree is in the range `[0, 104]`.
+*   `-100 <= Node.val <= 100`
+
+https://leetcode.com/problems/maximum-depth-of-binary-tree

0104_maximum-depth-of-binary-tree/python3/dfs-pre-order-global.py

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+# Time: O(N)
+# Space: O(N)
+
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    maxDepthValue = 0
+    
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        '''
+        Recursive DFS pre-order but storing max globally
+        '''
+        def findMax(node, depth):
+            if node is None: return None
+            
+            currDepth = depth + 1
+            self.maxDepthValue = max(currDepth, self.maxDepthValue)
+            findMax(node.left, currDepth)
+            findMax(node.right, currDepth)
+        
+        findMax(root, 0)
+        
+        return self.maxDepthValue

0104_maximum-depth-of-binary-tree/python3/dfs-pre-order-oneliner.py

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+# Time: O(N)
+# Space: O(N)
+
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    maxDepthValue = 0
+    
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        '''
+        Recursive DFS
+        '''
+        return 0 if root is None else 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))