graph-builder/markdown/graph-builder.traverser.depthfirstpreorder.md

A graph builder library for modeling abstract graph structures.

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# Traverser.depthFirstPreOrder method

Returns an unmodifiable `Iterable` over the nodes reachable from `startNode`<!-- -->, in the order of a depth-first pre-order traversal. "Pre-order" implies that nodes appear in the `Iterable` in the order in which they are first visited.

**Signature:**
```javascript
depthFirstPreOrder(...startNodes: Array<N>): Iterable<N>;
```
**Returns:** `Iterable<N>`

## Remarks

<b>Example:</b> The following graph with `startNode` `a` would return nodes in the order `abecfd` (assuming successors are returned in alphabetical order).
```
b ---- a ---- d
|      |
|      |
e ---- c ---- f

```
The behavior of this method is undefined if the nodes, or the topology of the graph, change while iteration is in progress.

The returned `Iterable` can be iterated over multiple times. Every iterator will compute its next element on the fly. It is thus possible to limit the traversal to a certain number of nodes as follows:
```
Iterables.limit(
    Traversers.forGraph(graph).depthFirstPreOrder(node), maxNumberOfNodes);

```
See <a href="https://en.wikipedia.org/wiki/Depth-first_search">Wikipedia</a> for more info.

Throws IllegalArgumentException if `startNode` is not an element of the graph.

## Parameters

|  Parameter | Type | Description |
|  --- | --- | --- |
|  `startNodes` | `Array<N>` |  |