Tree

Tree in Javascript (and Typescript).

Please read the wikipedia article on trees - computer science.

Install

npm i @jlguenego/tree

This library exposes both:

• ES2015 module that can be tree-shaked by Webpack for Angular etc.
• CommonJS module for traditionnal node way.

It is ready to use for both browsers and node app.

Usage

Instantiation

From an adjacency list

Sometimes, the simplest way to represent a tree is to give an object where each property key represents each node, and the corresponding value is its children.

const adjList: AdjacencyList = {
  1: ['2', '3', '4'],
  2: ['5', '6'],
  6: ['7', '8'],
};

const tree = Tree.fromAdjencyList(adjList);
console.log('tree: ', tree);

If the node are not string, but more complex object, we can do like this:

const adjList: AdjacencyList = {
  1: ['2', '3', '4'],
  2: ['5', '6'],
  6: ['7', '8'],
};
const nodeMap = ([
  '',
  'lorem',
  'ipsum',
  'dolor',
  'sit',
  'amet',
  'consectetur',
  'adipiscing',
  'elit',
] as unknown) as NodeMap<string>;

const tree = Tree.fromAdjacencyListAndNodeMap(adjList, nodeMap);
console.log('tree: ', tree);

From an object

const expectedTree = Tree.fromObject({
  node: '1',
  children: [
    {
      node: '2',
      children: [
        {node: '5'},
        {node: '6', children: [{node: '7'}, {node: '8'}]},
      ],
    },
    {node: '3'},
    {node: '4'},
  ],
});

From the constructor

To build a tree with no child:

const tree = new Tree<number>(23);

To build a tree with some children :

const tree = new Tree<number>(23, [
  new Tree<number>(12),
  new Tree<number>(13),
  new Tree<number>(7),
]);

This above example creates a tree with a root node (23) and 3 children leaf with 12, 13 and 7.

Reading tree structure

A tree is just a class instance with 2 attributes:

• node: representing the node value
• children: reprensenting the node children.

Converting the tree to a simple object

tree.toObject();

Tree API

A tree class instance has following methods:

Read only methods

• isBranch(): Test if the tree has at least one child.
• isLeaf(): Test if the tree has no child.
• flatten(): Returns a list of all leaf node values.
• getLeaves(): Returns a list of all leaf subtrees.
• enumerateDepthFirst(): Returns a list of all branches and leaves values (a child is completely recursively visited before processing the other children).
• enumerateBreadthFirst(): Returns a list of all branches and leaves values (all the first level children are first listed, then all the second level, and so on.).
• clone(): returns a shallow clone of the tree. All the structure is duplicated but the node values are not cloned.
• find(cb: (subtree)=> boolean): Find the first subtree satisfying criteria specified by cb.
• getPath(subtree): Retrieve the path of the subtree in the tree. Return an number[]if found with the children indexes, orundefined` if not found.
• getSubtree(path): Returns the subtree matching the path if possible. Can throw error if bad path.

Modifying methods

• graft(stock, scion, index?): add a subtree (scion) to the tree (stock). Index can optionally be specified to indicate where to add the scion between the children.

Search

This module give tools to perform Breadth-First-Search and Depth-First-Search, in a synchronous way and asynchronous way:

• BFSTree: class for doing synchronous Breadth-First-Search.
• BFSTreeAsync: class for doing asynchronous Breadth-First-Search.
• DFSTree: class for doing synchronous Depth-First-Search.
• DFSTreeAsync: class for doing asynchronous Depth-First-Search.

Each class has the same interface:

1. Instantiate the class by giving the Tree Trunk initialValue, the test method to check if the subtree is found, and the getChildren function for getting (or generating) the subree children if the subtree is not the searched one.
2. Call the search() method to return the searched node value subtree if it exists or undefined if not.

For asynchronous class, there is :

• an observable (called subject) that can be subscribed to get some info about the search progression. See the famous RxJS library.
• the interrupt() method to stop searching.

Example

The example is done with Breadth-First-Search. Just repleace BFSTree with DFSTree if you want Depth-First-Search.

Synchronous

const test = (n: number) => n > 10;
const getChildren = (n: number) => [n + 1, n + 2, n + 3];
const bfsTree = new BFSTree<number>(3, test, getChildren);
const result = bfsTree.search();
assert.deepStrictEqual(result, 11);

Asynchronous

async function main() {
    this.timeout(20000);
    const test = async (n: number) => n > 30;
    const getChildren = async (n: number) => {
      await sleep(10);
      return [n + 1, 2 * n + 1];
    };
    const bfsTree = new BFSTreeAsync<number>(1, test, getChildren);
    bfsTree.subject.subscribe(info => {
      console.log('info: ', inspect(info, false, null));
    });
    const result = await bfsTree.search();
    assert.deepStrictEqual(result, 31);
  });
}
main();

Participating

Do not hesitate to bring your contribution to this project. Fork and Pull Request are welcome.

License

ISC

Author

Jean-Louis GUENEGO jlguenego@gmail.com