JavaScript Trie implementation (ES2015+).

trie.js

/*
MIT License

Copyright (c) 2019 Fabio Forni

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

class Node {
	constructor() {
		this._children = new Map()
		// isLeaf tells whether this node completes an element
		this.isLeaf = false
	}

	child(item) {
		return this._children.get(item)
	}

	children() {
		return this._children.entries()
	}

	addChild(item) {
		this._children.set(item, new Node())
	}

	hasChild(item) {
		return this._children.has(item)
	}

	hasChildren() {
		return this._children.size > 0
	}

	removeChild(item) {
		return this._children.delete(item)
	}
}


class Trie {
	constructor() {
		this.root = new Node()
	}

	add(list) {
		var node = this.root
		for (const item of list) {
			if (!node.hasChild(item)) {
				node.addChild(item)
			}
			node = node.child(item)
		}
		// Last element has been reached, so this last node is leaf
		node.isLeaf = true
	}

	has(list) {
		const lastNode = (list) => {
			var node = this.root
			for (const item of list) {
				if (!node.hasChild(item)) {
					return null
				}
				node = node.child(item)
			}
			if (node.isLeaf) {
				return node
			}
			return null
		}

		return lastNode(list) !== null
	}

	remove(list) {
		var node = this.root
		var chain = []
		for (const item of list) {
			if (!node.hasChild(item)) {
				return false
			}
			node = node.child(item)
			chain.push(node)
		}
		// Here, list[i] has the value of the node in chain[i]
		for (var i = chain.length - 1; i >= 0; i--) {
			node = chain[i]
			if (node.isLeaf) {
				if (!node.hasChildren()) {
					chain[i - 1].removeChild(list[i])
				} else {
					node.isLeaf = false
				}
			} else if (!node.hasChildren()) {
				chain[i - 1].removeChild(list[i])
			}
		}
	}

	traverse() {
		const traverse = (node, value, path, pathList) => {
			path.push(value)
			if (node.isLeaf) {
				let pathClone = [...path]
				pathClone.shift()
				pathList.push(pathClone)
			}
			for (const [value, next_node] of node.children()) {
				traverse(next_node, value, path, pathList)
			}
			path.pop()
		}

		var paths = []
		traverse(this.root, undefined, [], paths)
		return paths
	}
}


module.exports = { Trie: Trie, }