Errata: Data Structures and Algorithms Book!

[kirupa]

LinkedList - remove and addAfter methods do not properly update the tail pointer

Huge thanks to @timfrobisher for pointing this out! The corrected form of this code can be seen here: kirupa/data_structures_algorithms/linkedlist.htm at master · kirupa/kirupa · GitHub

Full code pasted below:

class LinkedListNode {
  constructor(data, next = null) {
    this.data = data;
    this.next = next;
  }
}

class LinkedList {
  constructor() {
    this.head = null;
    this.tail = null;
    this.size = 0;
  }

  addFirst(data) {
    const newNode = new LinkedListNode(data, this.head);

    this.head = newNode;

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

    this.size++;
  }

  addLast(data) {
    const newNode = new LinkedListNode(data);

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

    this.size++;
  }

  addBefore(beforeData, data) {
    const newNode = new LinkedListNode(data);

    if (this.size === 0) {
      this.head = newNode;
      this.size++;
      return;
    }

    if (this.head.data === beforeData) {
      newNode.next = this.head;
      this.head = newNode;
      this.size++;
      return;
    }

    let current = this.head.next;
    let prev = this.head;

    while (current) {
      if (current.data === beforeData) {
        newNode.next = current;
        prev.next = newNode;
        this.size++;
        return;
      }

      prev = current;
      current = current.next;
    }

    throw new Error(`Node with data '${beforeData}' not found in list`);
  }

  addAfter(afterData, data) {
    const newNode = new LinkedListNode(data);

    if (this.size === 0) {
      this.head = newNode;
      this.size++;
      return;
    }

    let current = this.head;

    while (current) {
      if (current.data === afterData) {
        newNode.next = current.next;

        if (current === this.tail) {
          this.tail = newNode;
        }

        current.next = newNode;
        this.size++;
        return;
      }

      current = current.next;
    }

    throw new Error(`Node with data '${afterData}' not found in list!`);
  }

  contains(data) {
    let current = this.head;

    while (current) {
      if (current.data === data) {
        return true;
      }

      current = current.next;
    }

    return false;
  }

  removeFirst() {
    if (!this.head) {
      throw new Error('List is empty');
    }

    this.head = this.head.next;
    if (!this.head) {
      this.tail = null;
    }
    this.size--;
  }

  removeLast() {
    if (!this.tail) {
      throw new Error('List is empty');
    }

    if (this.head === this.tail) {
      this.head = null;
      this.tail = null;
      this.size--;
      return;
    }

    let current = this.head;
    let prev = null;

    while (current.next) {
      prev = current;
      current = current.next;
    }

    prev.next = null;
    this.tail = prev;
    this.size--;
  }

  remove(data) {
    if (this.size === 0) {
      throw new Error("List is empty");
    }

    if (this.head.data === data) {
      this.head = this.head.next;
      this.size--;
      return;
    }

    let current = this.head;

    while (current.next) {
      if (current.next.data === data) {
        if (current.next === this.tail) {
          this.tail = current;
        }
        current.next = current.next.next;
        this.size--;
        return;
      }

      current = current.next;
    }

    throw new Error(`Node with data '${data}' not found in list!`);
  }

  toArray() {
    const arr = [];

    let current = this.head;

    while (current) {
      arr.push(current.data);
      current = current.next;
    }

    return arr;
  }

  get length() {
    return this.size;
  }
}

let letters = new LinkedList();
letters.addLast("A");
letters.addLast("B");
letters.addLast("C");
letters.addLast("D");
letters.addLast("E");

console.log(letters.toArray()); // ['A', 'B', 'C', 'D', 'E']

letters.addFirst("AA");
letters.addLast("Z");

console.log(letters.toArray()); // ['AA', 'A', 'B', 'C', 'D', 'E', 'Z']

letters.remove("C");
letters.removeFirst();
letters.removeLast();

console.log(letters.toArray()); // ['A', 'B', 'D', 'E']

letters.addAfter("D", "Q");

console.log(letters.toArray()); // ['A', 'B', 'D', 'Q', 'E']

letters.addAfter("Q", "H");
letters.addBefore("A", "5");

console.log(letters.toArray()); // ['5', 'A', 'B', 'D', 'Q', 'H', 'E']

letters.remove("E");

console.log(letters.toArray()); // ['5', 'A', 'B', 'D', 'Q', 'H']

console.log(letters.length); // 7

letters.addAfter("H", "Z");