revert a list

revert.cs

using System;

namespace hello_csharp
{
    class Program
    {
        class Node
        {
            public int val;
            public Node next;

            public Node(int val, Node next = null)
            {
                this.val = val;
                this.next = next;
            }
        }


        static void Main(string[] args)
        {
            // construct a list (1 -> 2 -> 3 -> 4 -> 5 -> NULL)
            var head = new Node(1);
            var prv = head;

            for (var i = 2; i <= 5; i++)
            {
                var node = new Node(i);
                prv.next = node;
                prv = node;
            }

            Print(head);

            // reverse the list (1 <- 2 <- 3 <- 4 <- 5 <- NULL)
            prv = null;
            var cur = head;
            while (cur != null)
            {
                var node = cur.next;

                cur.next = prv;
                prv = cur;
                cur = node;
            }

            head = prv; // new the head of list

            Print(head);
        }

        // print the list
        static void Print(Node head)
        {

            var cur = head;
            while (cur != null)
            {
                Console.Write($"{cur.val}  ");
                cur = cur.next;
            }

            Console.WriteLine();
        }
    }
}