Linked List

linked_list.js

class Node {
  constructor(value = null, next = null) {
    this.value = value;
    this.next = next;
  }
}

class List {
  constructor() {
    this.head = null;
    this.tail = null;
    this.length = 0;
  }

  append(value) {
    const newNode = new Node(value);

    if (!this.head) {
      this.head = newNode;
      this.tail = this.head;
    } else {
      this.tail.next = newNode;
      this.tail = newNode;
    }

    ++this.length;

    return this;
  }

  prepend(value) {
    const newNode = new Node(value, this.head);

    if (!this.head) {
      this.tail = newNode;
    }

    this.head = newNode;

    ++this.length;

    return this;
  }

  pop() {
    if (!this.head) {
      return null;
    }

    let node = this.head;
    let prev = null;
    while (node.next) {
      prev = node;
      node = node.next;
    }

    const value = node.value;
    this.tail = prev;
    if (prev) {
      prev.next = null;
    } else {
      this.head = null;
    }

    --this.length;

    return value;
  }

  shift() {
    if (!this.head) {
      return null;
    }

    const value = this.head.value;
    this.head = this.head.next;
    if (!this.head) {
      this.tail = null;
    }

    --this.length;

    return value;
  }

  insert(index, value) {
    if (index < -1 || this.length <= index) {
      return this;
    }

    if (!this.head || index == -1) {
      return this.prepend(value);
    }

    let node = this.head;
    while (index > 0) {
      node = node.next;
      --index;
    }

    const newNode = new Node(value, node.next);
    node.next = newNode;

    ++this.length;

    return this;
  }

  remove(index) {
    if (!this.head || index < 0 || this.length <= index) {
      return null;
    }

    --index;
    if (index < 0) {
      this.shift();
      return this;
    }

    let node = this.head;
    while (index > 0) {
      node = node.next;
      --index;
    }

    if (node.next == this.tail) {
      this.tail = node;
    }
    node.next = node.next.next;
    --this.length;

    return node;
  }

  to_array() {
    const array = [];
    let node = this.head;
    while (node) {
      array.push(node.value);
      node = node.next;
    }
    return array;
  }
}