Added the first Tree question

Twopointer/Binary search/Linked List/Trees/104. Maximum Depth of Binary Tree.py

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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:
+
+
+Input: root = [3,9,20,null,null,15,7]
+Output: 3
+Example 2:
+
+Input: root = [1,null,2]
+Output: 2
+'''
+'''DFS and recursive way: '''
+
+# 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:
+    def maxDepth(self, root: TreeNode) -> int:
+        if root is None:  # base case
+            return 0
+        else:
+            left_height = self.maxDepth(root.left)
+            right_height = self.maxDepth(root.right)
+            return max(left_height, right_height) + 1
+
+
+            # BFS iterative way
+            # Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    def maxDepth(self, root: TreeNode) -> int:
+        if not root:
+            return 0
+
+        queue = [(root, 1)]
+        while queue:
+            node, level = queue.pop(0)
+            if node.left:
+                queue.append((node.left, level + 1))
+            if node.right:
+                queue.append((node.right, level + 1))
+
+        return level
+