NIST

level-order traversal

(algorithm)

Definition: Process all nodes of a tree by depth: first the root, then the children of the root, etc. Equivalent to a breadth-first search from the root.

See also postorder traversal, preorder traversal, tree traversal, level.

Note: For instance, if the "processing" is just printing, a tree is printed as "root, all children of the root, all grandchildren (children of children) of the root, etc." Here is pseudocode for an inefficient level-order traversal of a binary tree: 

 levelorderAux(tree, level)
 begin
     if tree is null, return;

     if level is 1, then
         print(tree.root);
     else if level greater than 1, then
         levelorderAux(tree.left_subtree, level-1);
         levelorderAux(tree.right_subtree, level-1);
     endif
 end
 
 levelorder(tree)
 begin
     for d = 1 to height(tree)
         levelorderAux(tree, d);
     endfor
 end

See [Stand98, p. 251].

Author: PEB

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 26 May 2011.
HTML page formatted Mon Feb 2 13:10:39 2015.

Cite this as:
Paul E. Black, "level-order traversal", in Dictionary of Algorithms and Data Structures [online], Vreda Pieterse and Paul E. Black, eds. 26 May 2011. (accessed TODAY) Available from: http://www.nist.gov/dads/HTML/levelOrderTraversal.html