给定一个链表: 1->2->3->4->5, 和 n = 2.

当删除了倒数第二个节点后，链表变为 1->2->3->5.

/**
 * @param {ListNode} head
 * @param {number} n
 * @return {ListNode}
 */
let removeNthFromEnd = function (head, n) {
  let node = head
  let nodes = []
  do {
    nodes.push(node)
    node = node.next
  } while (node)

  const l = nodes.length
  const index = l - n
  const targetNode = nodes[index]
  const prevNode = nodes[index - 1]
  if (prevNode) {
    prevNode.next = targetNode.next
  }

  const tempNext = targetNode.next
  targetNode.next = null

  if (targetNode === head) {
    return tempNext
  }
  return head
}