Create lowest_common_ancestor.py

trees_and_graphs/lowest_common_ancestor.py

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+'''
+Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.
+'''
+
+class ThisTree:
+    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
+        
+        def dfs(root, p, q):
+
+            if not root:
+                return False
+            
+            left = dfs(root.left, p, q)
+            right = dfs(root.right, p, q)
+            mid = root == p or root == q
+
+            if mid + left + right >= 2:
+                self.answer = root
+            
+            return left or right or mid
+                
+        dfs(root, p, q)
+        
+        return self.answer
+