0206-reverse-linked-list.go

/**
 * 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
	}

	reversedListHead := reverseList(head.Next)
	head.Next.Next = head
	head.Next = nil
	return reversedListHead
}

// Iterative version
// func reverseList(head *ListNode) *ListNode {
//     var prev *ListNode
//     curr := head
//
//     for curr != nil {
//         tmp := curr.Next
//         curr.Next = prev
//         prev = curr
//         curr = tmp
//     }
//
//     return prev
// }