Also known as level-order traversal when applied to trees.

It starts at a node and explores all its immediate neighbors before moving on to child nodes.

Also known as depth-first search.

It starts at a node and explores as for as possible along one branch before backtracking to other branches.

Visit first root and then children.

preorder(node):
  if node is null:
    return

  visit(node)
  preorder(node.left)
  preorder(node.right)

Visit first left child, then root, finally right child. Put root in-between children.

inorder(node):
  if node is null:
    return

  inorder(node.left)
  visit(node)
  inorder(node.right)

Visit first left child, then right child, finally the root. Put root after children.

postorder(node):
  if node is null:
    return

  postorder(node.left)
  postorder(node.right)
  visit(node)