There are three traditional tree traversals for binary trees: preorder, postorder, and inorder. For general trees, preorder and postorder traversals are defined with meanings similar to their binary tree counterparts. Preorder traversal of a general tree first visits the root of the tree, then performs a preorder traversal of each subtree from left to right. A postorder traversal of a general tree performs a postorder traversal of the root’s subtrees from left to right, then visits the root. Inorder traversal does not have a natural definition for the general tree, because there is no particular number of children for an internal node. An arbitrary definition—such as visit the leftmost subtree in inorder, then the root, then visit the remaining subtrees in inorder—can be invented. However, inorder traversals are generally not useful with general trees.
