# Tree - Order

### Table of Contents

## About

The term tree order describes how a tree is traversed.

It can also be a graph data structures, selecting an arbitrary node as the root.

## Type

```
h
/ | \
/ | \
d e g
/|\ |
/ | \ f
a b c
```

The traversals are classified by the order in which the nodes are visited:

- breadth-first order (hdegabcf). known also as breadht-first search
^{1)}- All the nodes of depth 0 are returned, then depth 1, then 2, and so on. - closest-first order (degcfab)
- depth-first order
- pre-order left (h d a b c e g f),
- pre-order right (h g f e d c b a)
- post-order left (a b c d e f g h),

Not for a tree (directed algorithm)

## Example

### Java

- Impkement a Guava tree traverser

```
/* Node is an object of your implementation with a getChildren function */
TreeTraverser<Node> traverser = new TreeTraverser<Node>() {
@Override
public Iterable<Task> children(Object node) {
return node.getChildren();
}
};
Node root = ....
```

Then you can iterate over the tree with a for loop:

- in breadth-first order

`for (Task task : traverser.breadthFirstTraversal(root)) { ... }`

- in Preorder

`for (Task task : traverser.preOrderTraversal(root)) { ... }`

- in postorder

`for (Task task : traverser.postOrderTraversal(root)) { ... }`

## Documentation / Reference

^{1)}