5.2: Sample implementations for Tree Traversal

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preorder(node)
 visit(node)
 if node.left ≠ null then preorder(node.left)
 if node.right ≠ null then preorder(node.right)

inorder(node)
 if node.left ≠ null then inorder(node.left)
 visit(node)
 if node.right ≠ null then inorder(node.right)

postorder(node)
 if node.left ≠ null then postorder(node.left)
 if node.right ≠ null then postorder(node.right)
 visit(node)

levelorder(root)
 queue<node> q
 q.push(root)
 while not q.empty do
  node = q.pop
  visit(node)
  if node.left ≠ null then q.push(node.left)
  if node.right ≠ null then q.push(node.right)

For an algorithm that is less taxing on the stack, see Threaded Trees.