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Posts Tagged ‘non-binary tree’

Four Traversal Patterns for Tree<T>

Posted by Dan Vanderboom on April 5, 2010

[Updated 8/14/2014] The source code for this library can be found here at GitHub. Also check out my blog post announcing it.

This is an update to my original article on a non-binary tree data structure.  After receiving multiple requests to complete this, here it is.  The updated source code can be downloaded here.

To illustrate the four possible traversal types, the following tree data structure will be used in all of my examples.


The enum TreeTraversalType has two possible values: DepthFirst and BreadthFirst.  The other enum involved, TreeTraversalDirection, determines which end of the tree it starts from: TopDown or BottomUp.  There are four possible combinations of these two values, which will each be presented separately.

Depth-First, Top-Down

This traversal strategy involves starting at the root and digging as deep into the tree whenever possible.  The order of nodes yielded by our example tree structure would be a-b-d-e-c-f-g.


Depth-First, Bottom-Up

Because we’re moving bottom-up in this case, the first thing we have to do is dive to the bottom of the first branch we find.  We skip past a and b, and find d with no children.  D is therefore the first node we’ll yield.  E is it’s peer, so that comes next.  From e, we move up the tree to b.  A is the root, so it has to be the last node yielded, so we’re going to dive into the c branch next, yield f and g, and then yield c and finally a.  The order is: d-e-b-f-g-c-a.


Breadth-First, Top-Down

When we traverse breadth-first, we’re moving through the tree in levels.  With Top-Down, we start with the root a, then move to the second level with b and c, and then finally move to the third level to yield d-e-f-g.


Breadth-First, Bottom-Up

The final traversal is the one I had the most trouble with, and I ended up cheating a little by reversing the Breadth-First, Top-Down traversal.



Now, with a call to GetEnumerable on a node object, you can specify which of these four traversal patterns to use.  Here is an example of how that code looks:

foreach (SimpleTreeNode<string> node in 
    root.GetEnumerable(TreeTraversalType.DepthFirst, TreeTraversalDirection.TopDown))
    // ...



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