misc: restructure contents

experimental/utilities/python/tree_traversal.py

@@ -0,0 +1,62 @@
+# Various iterative ways of traversing a tree.
+def inorder_traversal(root):
+    """
+    :type root: TreeNode
+    :rtype: List[int]
+    """
+    if not root:
+      return []
+    result = []
+    stack = [root]
+    while len(stack) > 0:
+        curr_node = stack.pop()
+        if curr_node.left:
+            stack.append(curr_node)
+            stack.append(curr_node.left)
+            curr_node.left = None
+        else:
+            result.append(curr_node.val)
+            if curr_node.right:
+                stack.append(curr_node.right)
+    return result
+
+def preorder_traversal(root):
+    """
+    :type root: TreeNode
+    :rtype: List[int]
+    """
+    if not root:
+        return []
+    result = []
+    stack = [root]
+    while len(stack) > 0:
+        curr_node = stack.pop()
+        result.append(curr_node.val)
+        if curr_node.right:
+            stack.append(curr_node.right)
+        if curr_node.left:
+            stack.append(curr_node.left)
+    return result
+
+def postorder_traversal(root):
+    """
+    :type root: TreeNode
+    :rtype: List[int]
+    """
+    if not root:
+        return []
+    result = []
+    stack = [root]
+    while len(stack) > 0:
+        curr_node = stack.pop()
+        if curr_node.left:
+            stack.append(curr_node)
+            stack.append(curr_node.left)
+            curr_node.left = None
+        elif curr_node.right:
+            stack.append(curr_node)
+            stack.append(curr_node.right)
+            curr_node.right = None
+        else:
+            result.append(curr_node.val)
+    return result