/**
 *
 * Ashish Patel
 * e: ashishsushilPatel@gmail.com
 * w: https://ashish.me
 *
 */

/*
 * Reverse a singly linked list.
 *
 * Example:
 *
 * Input: 1->2->3->4->5->NULL
 * Output: 5->4->3->2->1->NULL
 * Follow up:
 *
 * A linked list can be reversed either iteratively or recursively. Could you implement both?
 */

function ListNode(val) {
  this.val = val
  this.next = null
}

function reverseLinkedList(val) {
  let currentHead = val
  let previousHead = null
  while (currentHead) {
    let swap = currentHead.next
    currentHead.next = previousHead
    previousHead = currentHead
    currentHead = swap
  }
  return previousHead
}

test('reverse Linked List', () => {
  const ll1 = new ListNode(1)
  ll1.next = new ListNode(2)
  ll1.next.next = new ListNode(3)
  ll1.next.next.next = new ListNode(4)
  ll1.next.next.next.next = new ListNode(5)

  const ll2 = new ListNode(5)
  ll2.next = new ListNode(4)
  ll2.next.next = new ListNode(3)
  ll2.next.next.next = new ListNode(2)
  ll2.next.next.next.next = new ListNode(1)
  expect(reverseLinkedList(ll1)).toEqual(ll2)
})