singlyLinkedList.js

////////////////   Singly Linked Lists and methods /////////////////

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

class singlyLinkedList {
  constructor() {
    this.head = null;
    this.tail = null;
    this.length = 0;
  }
  push(val) {
    let newNode = new Node(val);
    if (!this.head) {
      this.head = newNode;
      this.tail = this.head;
    } else {
      this.tail.next = newNode;
      this.tail = newNode;
    }
    this.length++;
    return this;
  }

  pop() {
    if (!this.head) return undefined;

    let current = this.head;
    let newTail = current;
    while (current.next) {
      newTail = current;
      current = current.next;
    }
    this.tail = newTail;
    this.tail.next = null;
    this.length--;
    if (this.length === 0) {
      this.head = null;
      this.tail = null;
    }
    return current;
  }

  shift() {
    if (!this.head) return undefined;
    let currentHead = this.head;
    this.head = currentHead.next;
    this.length--;
    if (this.length === 0) {
      this.tail = null;
    }
    return currentHead;
  }
  unshift(val) {
    let newNode = new Node(val);
    if (!this.head) {
      this.head = newNode;
      this.tail = newNode;
    } else {
      newNode.next = this.head;
      this.head = newNode;
    }
    this.length++;
    return this;
  }

  get(index) {
    if (index < 0 || index >= this.length) return null;
    let counter = 0;
    let current = this.head;
    while (counter !== index) {
      current = current.next;
      counter++;
    }
    return current;
  }

  set(index, val) {
    let foundNode = this.get(index);
    if (foundNode) {
      foundNode.val = val;
      return true;
    }
    return false;
  }
  insert(index, val) {
    if (index < 0 || index > this.length) return false;
    if (index === this.lenght) {
      this.push(val);
      return true;
    }
    if (index === 0) {
      this.unshift(val);
      return true;
    }
    let newNode = new Node(val);
    let prev = this.get(index - 1);
    let aft = prev.next;
    prev.next = newNode;
    newNode.next = aft;
    this.length++;
    return true;
  }

  remove(index) {
    if (index < 0 || index > this.length) return undefined;
    if (index === this.lenght - 1) return this.pop();
    if (index === 0) return this.shift();
    let prevNode = this.get(index - 1);
    let removed = prevNode.next;
    prevNode.next = removed.next;
    this.length--;
    return removed;
  }

  reverse() {
    let node = this.head;
    this.head = this.tail;
    this.tail = node;
    let prev = null,
      next;

    for (let i = 0; i < this.length; i++) {
      next = node.next;
      node.next = prev;
      prev = node;
      node = next;
    }
    return this;
  }

  print() {
    let arr = [];
    let current = this.head;
    while (current) {
      arr.push(current.val);
      current = current.next;
    }
    console.log(arr);
  }
}

// let list = new singlyLinkedList();
// list.push("HELLO");
// list.push("WORLD");
// list.push("HOW");
// list.push("ARE");
// console.log(list.push("YOU")); //singlyLinkedList {
// head: Node { val: 'HELLO', next: Node { val: 'WORLD', next: [Node] } },
// tail: Node { val: 'YOU', next: null },
// length: 5 }

// // list.shift();
// // list.unshift("HHH");
// // // console.log(list);
// // list.set(0, "ME");
// // list.insert(1, "AU");
// // list.remove(1);
// list.reverse(); // [ 'YOU', 'ARE', 'HOW', 'WORLD', 'HELLO' ]

// console.log(list.print()); //   [ 'HELLO', 'WORLD', 'HOW', 'ARE', 'YOU' ]