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206. Reverse Linked List	Reverse Linked List	2023-01-22 21:20:00 +0800	2023-01-22 21:20:00 +0800	false	Kimi.Tsai	https://kimi0230.github.io/	Reverse Linked List			LeetCode Go Easy Reverse Linked List	LeetCode			false	false	false	true	true	true	true	false	false	enable auto true true	copy maxShownLines true 200	enable		enable true	enable true	css js	images

206. Reverse Linked List

題目

Given the head of a singly linked list, reverse the list, and return the reversed list.

Example 1:

Input: head = [1,2,3,4,5]
Output: [5,4,3,2,1]

Example 2:

Input: head = [1,2]
Output: [2,1]

Example 3:

Input: head = []
Output: []

Constraints:

• The number of nodes in the list is the range [0, 5000].
• -5000 <= Node.val <= 5000

Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?

題目大意

將 Linked List 反向

解題思路

來源

• https://leetcode.com/problems/Reverse Linked List/

解答

https://github.com/kimi0230/LeetcodeGolang/blob/master/Leetcode/0000.kkkk/main.go

package reverselinkedlist

import (
	. "LeetcodeGolang/structures"
)

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */

func ReverseList(head *ListNode) *ListNode {
	if head == nil || head.Next == nil {
		return head
	}

	var prev *ListNode

	for head != nil {
		next := head.Next
		head.Next = prev
		prev = head
		head = next
	}

	return prev
}

func ReverseListRecursively(head *ListNode) *ListNode {
	return ListRecursivelyChild(head, nil)
}

func ListRecursivelyChild(current *ListNode, prev *ListNode) *ListNode {
	if current == nil {
		return prev
	}
	next := current.Next
	current.Next = prev
	return ListRecursivelyChild(next, current)
}

Benchmark

goos: darwin
goarch: amd64
pkg: LeetcodeGolang/Leetcode/0206.Reverse-Linked-List
cpu: Intel(R) Core(TM) i5-8259U CPU @ 2.30GHz
BenchmarkReverseList-8                  1000000000               0.7960 ns/op          0 B/op          0 allocs/op
BenchmarkReverseListRecursively-8       276534334                4.374 ns/op           0 B/op          0 allocs/op
PASS
ok      LeetcodeGolang/Leetcode/0206.Reverse-Linked-List        2.597s