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61_RotateList.swift
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61_RotateList.swift
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//
// 61. 旋转链表
//
// 给定一个链表,旋转链表,将链表每个节点向右移动 k 个位置,其中 k 是非负数。
//
// 题目链接:https://leetcode-cn.com/problems/rotate-list/
// 标签:链表、双指针
// 要点:链表成环,区分判断好`head`与`tail`
// 时间复杂度:O(N)
// 空间复杂度:O(1)
//
import Foundation
/// Definition for singly-linked list.
public class ListNode {
public var val: Int
public var next: ListNode?
public init(_ val: Int) {
self.val = val
self.next = nil
}
}
class Solution {
func rotateRight(_ head: ListNode?, _ k: Int) -> ListNode? {
guard let head = head else { return nil }
guard head.next != nil else { return head }
var node = head
var n = 1
while node.next != nil {
node = node.next!
n += 1
}
node.next = head
var newTail = head
for _ in 0..<(n - k % n - 1) {
newTail = newTail.next!
}
let newHead = newTail.next
newTail.next = nil
return newHead
}
}
/**
示例1:
```
输入: 1->2->3->4->5->NULL, k = 2
输出: 4->5->1->2->3->NULL
解释:
向右旋转 1 步: 5->1->2->3->4->NULL
向右旋转 2 步: 4->5->1->2->3->NULL
```
示例 2:
```
输入: 0->1->2->NULL, k = 4
输出: 2->0->1->NULL
解释:
向右旋转 1 步: 2->0->1->NULL
向右旋转 2 步: 1->2->0->NULL
向右旋转 3 步: 0->1->2->NULL
向右旋转 4 步: 2->0->1->NULL
```
*/