剑指06.从尾到头打印链表

输入一个链表的头节点，从尾到头反过来返回每个节点的值（用数组返回）。

输入：head = [1,3,2]
输出：[2,3,1]

解答

1. reverse()

var reversePrint = function (head) {
  if (head === null) return []
  const res = []
  while (head) {
    res.push(head.val)
    head = head.next
  }
  return res.reverse()
}

2. 反转链表

// 首先将链表反转
function reverseLink(head) {
  if (head === null || head.next === null) return head
  let p = head.next
  head.next = null
  let tmp = null
  while (p !== null) {
    tmp = p.next // tmp 指针前进（保存下一个指针信息）
    p.next = head // 指针反转
    head = p // head 指针前进
    p = tmp // p 指针前进
  }
  return head
}

3. 递归反转链表

function reverseLink(head) {
  if (head === null || head.next === null) return head
  const p = reverseLink(head.next)
  head.next.next = head // 指针反转
  head.next = null
  return p // 返回真正的表头
}