preorder traversal

(algorithm)

Definition: Process all nodes of a tree by processing the root, then recursively processing all subtrees.

Also known as prefix traversal.

Generalization (I am a kind of ...)
tree traversal, depth-first search.

Note: For instance, if the "processing" is just printing, a tree is printed as "root (first subtree) (second subtree) ... (last subtree)." Here is pseudocode for a binary tree:

 preorder(tree)
 begin
     if tree is null, return;

     print(tree.root);
     preorder(tree.left_subtree);
     preorder(tree.right_subtree);
 end

Author: PEB

Implementation

Mukundan's animation (Java).

Go to the Dictionary of Algorithms and Data Structures home page.

If you have suggestions, corrections, or comments, please get in touch with Paul Black.

Entry modified 14 August 2008.
HTML page formatted Mon Feb 2 13:10:40 2015.

Cite this as:
Paul E. Black, "preorder traversal", in Dictionary of Algorithms and Data Structures [online], Vreda Pieterse and Paul E. Black, eds. 14 August 2008. (accessed TODAY) Available from: http://www.nist.gov/dads/HTML/preorderTraversal.html