1. if the tree is empty, do nothing,
else:
(For preorder)
visit root
do left subtree
do right subtree

2. if the tree is empty, do nothing,
else:
(For inorder)
do left subtree
visit root
do right subtree

3. if the tree is empty, do nothing,
else:
(For postorder)
do left subtree
do right subtree
visit root

4. if the tree is empty, do nothing,
else:
(For preorder)
visit root
do left subtree
do right subtree
(For inorder)
(For postorder)

5. void pre-traverse(Treenode p)
{ Treenode-stack A;
Clear(A);
while (true)
if (p ≠ nil)
{ Visit(p);
Stack(A, p);
p ← p↑Llink; }
else
if (Empty(A))
return;
{ p ← Unstack(A);
p ← p↑Rlink;