package main
import "fmt"
// ListNode represents a node in a singly linked list.
type ListNode struct {
value int // data stored in the node
next *ListNode // pointer to the next node
}
// reverseList reverses a singly linked list in-place.
func reverseList(head *ListNode) *ListNode {
var prev *ListNode = nil // will become the new head
current := head // pointer to traverse the list
for current != nil {
nextNode := current.next // save next node
current.next = prev // reverse the link
prev = current // move prev forward
current = nextNode // move current forward
}
return prev // prev is the new head
}
// printList prints the linked list in a readable format.
func printList(head *ListNode) {
for temp := head; temp != nil; temp = temp.next {
fmt.Print(temp.value)
if temp.next != nil {
fmt.Print(" -> ")
}
}
fmt.Println()
}
func main() {
// Build a sample list: 1 -> 2 -> 3 -> 4 -> 5
head := &ListNode{value: 1}
head.next = &ListNode{value: 2}
head.next.next = &ListNode{value: 3}
head.next.next.next = &ListNode{value: 4}
head.next.next.next.next = &ListNode{value: 5}
fmt.Println("Original list:")
printList(head)
// Reverse the list
head = reverseList(head)
fmt.Println("Reversed list:")
printList(head)
}
/*
run:
Original list:
1 -> 2 -> 3 -> 4 -> 5
Reversed list:
5 -> 4 -> 3 -> 2 -> 1
*/
