practice problem

linked_list_photo_album_merge_sort.js

// -------------
// Instructions:
// -------------
//
// 1 create two linked lists sorted by date
// 2. create a new linked list (combined list)
// 3. compare head of list-01 with head of list-02 (currentNode = this.head)
// 4. if list-01.head < list-02.head 
// 5. add list-01.head to combined list (using add to tail method)
// 6. traversing list-01

// ------------
// Constraints:
// ------------
//
// 1. Don't mutate the original lists??

// ------------
// Explanation:
// ------------
//
// list-01
// 1 -> 2 -> 6 -> null
// list-02
// 3 -> 5 -> [ 7 -> 9 -> null ]
// combined list
// 1 -> 2 -> 3 -> 5 -> 6 -> 7 -> 9 -> null

function combinedList(listOne, listTwo){

  // if both lists are empty
  let listOneCurrentNode = listOne.head;
  let listTwoCurrentNode = listTwo.head;

  if(!listOneCurrentNode){
    console.log('list one is empty')
  } else if(!listTwoCurrentNode){
    console.log('list two is empty')
  }

  // console.log(listOneCurrentNode.val)
  // console.log(listTwoCurrentNode.val)

  const combined = new linkedList(null, null) // error here, no parameters

  if(listOneCurrentNode.val <= listTwoCurrentNode.val){
    combined.addToTail(listOneCurrentNode);
    listOneCurrentNode = listOneCurrentNode.getNextNode(); // also works with .next
  } else {
    combined.addToTail(listTwoCurrentNode);
    listTwoCurrentNode = listTwoCurrentNode.getNextNode() // also works with .next
  }

  while(listOneCurrentNode && listTwoCurrentNode){
    if(listOneCurrentNode.val <= listTwoCurrentNode.val){
      combined.addToTail(listOneCurrentNode);
      listOneCurrentNode = listOneCurrentNode.next
    } else {
      combined.addToTail(listTwoCurrentNode);
      listTwoCurrentNode = listTwoCurrentNode.next
    }
  }

  if(listOneCurrentNode == null){
    combined.addToTail(listTwoCurrentNode);
    listTwoCurrentNode = listTwoCurrentNode.next
  } else if(listTwoCurrentNode == null){
    combined.addToTail(listOneCurrentNode);
    listOneCurrentNode = listOneCurrentNode.next
  }

  return combined.tail;
}


// -------------------------
// Given: Singly Linked List 
// -------------------------

class Node {
  constructor(val, next) {
    this.val = val;
    this.next = next; // error here, i had null
  }

  getNextNode(){
    return this.next;
  }
}

class linkedList {
  constructor(){
    this.head = null; // error here, i had head
    this.next = null;
    this.length = 0;
  }

  addToTail(val){
    const newNode = new Node(val);

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

    this.tail = newNode;
    this.length++;
    return this;
  }
}

const listOne = new linkedList()
const listTwo = new linkedList()

listOne.addToTail(1);
listOne.addToTail(2);
listOne.addToTail(6);

listTwo.addToTail(3);
listTwo.addToTail(5);
listTwo.addToTail(7);
listTwo.addToTail(9);

const result = combinedList(listOne, listTwo)
console.log(result)