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144-binary-tree-preorder-traversal/144-binary-tree-preorder-traversal.py

@@ -0,0 +1,30 @@
+# 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 preorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
+        # Base cases: no node or only root node
+        if root == None:
+            return []
+    
+        if root.left == None and root.right == None:
+            return [root.val]
+        
+        # Simple recursive solution: add to array as you traverse
+        visited = [root.val]    # First node in the order is the current one
+        
+        # All nodes to the left must be added next in the array
+        if root.left != None:
+            visited += self.preorderTraversal(root.left)
+            
+        # All nodes to the right must be added next in the array
+        if root.right != None:
+            visited += self.preorderTraversal(root.right)
+            
+        return visited
+        
+        
+