206-reverse-linked-list.cs

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution {
    public ListNode ReverseList(ListNode head) {
        if (head == null)
        {
            return null;
        }

        if (head.next == null)
        {
            return head;
        }

        var next = head.next;
        var last = ReverseList(next);
        next.next = head;
        head.next = null;
        return last;
    }
}