# 22.链表中倒数第k个节点

## 题目

输入一个链表，输出该链表中倒数第k个节点。为了符合大多数人的习惯，本题从1开始计数，即链表的尾节点是倒数第1个节点。

例如，一个链表有 6 个节点，从头节点开始，它们的值依次是 1、2、3、4、5、6。这个链表的倒数第 3 个节点是值为 4 的节点。

示例：

```cpp
 给定一个链表: 1->2->3->4->5, 和 k = 2.

 返回链表 4->5.
 通过次数193,790提交次数246,166
```

来源：力扣（LeetCode）

链接：<https://leetcode-cn.com/problems/lian-biao-zhong-dao-shu-di-kge-jie-dian-lcof>

著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

> [GitHub](https://github.com/RyukieSama/RyukiePlayground/blob/main/剑指Offer.playground/Pages/22.链表中倒数第k个节点.xcplaygroundpage/Contents.swift)

## 解法一：栈

```swift
func getKthFromEnd(_ head: ListNode?, _ k: Int) -> ListNode? {
    var node = head

    var temp: [ListNode] = []

    while let currentNode = node {
        temp.insert(currentNode, at: 0)
        if temp.count > k {
            temp.removeLast()
        }
        node = currentNode.next
    }

    return temp.last
}
```

## 解法二：差速双指针

```swift
 func getKthFromEnd(_ head: ListNode?, _ k: Int) -> ListNode? {
    var right: ListNode? = head, left: ListNode? = head

    // 移动到 第 k 个节点
    for _ in 0..<k-1 {
        right = right?.next
    }

    while let _ = right?.next {
        right = right?.next
        left = left?.next
    }

    return left
}
```


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