Reverse Doubly Linked List: Efficient Algorithm and Explanation

reverse() {
  let currNode = this.head; //current node starts at the head of the list
  let prevNode = null; //initialize previous node as null
  let nextNode = null; //initialize next node as null

  while (currNode) { //while there is a current node
    nextNode = currNode.next; //store the next node
    prevNode = currNode.previous; //store the previous node

    currNode.next = prevNode; //change the next node of the current node to link to the previous node
    currNode.previous = nextNode; //change the previous node of the current node to link to the next node

    prevNode = currNode; //move the previous node one step forward
    currNode = nextNode; //move the current node one step forward
  }

  this.tail = this.head; //reset the tail to the head
  this.head = prevNode; //reset the head to the last node (which is now the first node after reversing)

  return this;
}

This code implements a function to reverse a doubly linked list. It uses three pointers: currNode, prevNode, and nextNode. The algorithm works as follows:

1. Initialization:

   • currNode is initialized to the head of the list.
   • prevNode is initialized to null (since there is no node before the head).
   • nextNode is initialized to null.

2. Iteration:

   • The loop continues as long as there is a currNode (we haven't reached the end of the list).
   • Inside the loop:
     • The nextNode is stored to keep track of the node after the current one.
     • The prevNode is stored.
     • The next pointer of the currNode is changed to point to the prevNode (reversing the direction).
     • The previous pointer of the currNode is changed to point to the nextNode (reversing the direction).
     • The prevNode is updated to the current node, moving the prevNode one step forward.
     • The currNode is updated to the nextNode, moving the currNode one step forward.

3. Resetting Head and Tail:

   • After the loop, the tail is set to the head (which is now the last node of the reversed list).
   • The head is set to the prevNode (which is now the first node of the reversed list).

4. Return:

   • The function returns this, referring to the current list object after the reversal operation.