反转链表

package main
 
import "fmt"
 
type ListNode struct {
    Val  int
    Next *ListNode
}
 
func reverseList(head *ListNode) *ListNode {
    if head == nil || head.Next == nil {
        return head
    }
    newHead := reverseList(head.Next)
    head.Next.Next = head
    head.Next = nil
    return newHead
}
 
// reverseList 反转单链表
func reverseList2(head *ListNode) *ListNode {
    prev := nil
    curr := head
    for curr != nil {
        next := curr.Next // 先保存下一个节点
        curr.Next = prev // 将当前节点的 Next 指向前一个节点，实现反转
        prev = curr      // 移动 prev 和 curr 向前移动
        curr = next      //当前节点移到下一个
    }
    return prev // prev 将会是新链表的头节点
}

func main() {
    // 创建一个链表: 1 -> 2 -> 3 -> 4 -> 5
    head := &ListNode{Val: 1}
    temp := head
    for i := 2; i <= 5; i++ {
        temp.Next = &ListNode{Val: i}
        temp = temp.Next
    }
 
    // 翻转链表
    newHead := reverseList(head)
 
    // 打印翻转后的链表: 5 -> 4 -> 3 -> 2 -> 1
    for newHead != nil {
        fmt.Print(newHead.Val, " -> ")
        newHead = newHead.Next
    }
    fmt.Println()
}