LinkedLists.Reverse

optimal solution

    public ListNode Reverse(ListNode head){
        
        var node = head;
        ListNode prev = null;
        while(node != null){
            var next = node.next;
            node.next = prev;
            prev = node;
            node = next;
        }
        
        return prev;
    }

not optimal solution

    public ListNode ReverseList(ListNode head) {
        
        if (head == null)
            return null;
        
        ListNode current = head;
        var links = new List<ListNode>();
        ListNode lastNode = null;
        while (current != null){        
            if (current.next != null)
              links.Add(current);
            
            if (current.next == null)
                lastNode = current;
            
            current = current.next;
        }
                                 
        var reversedHead = lastNode;
        Console.WriteLine("lastNodeValue=" + lastNode.val);
        current = lastNode; 
        for (var i = links.Count() - 1; i >= 0; i -- ){            
          current.next = links[i];    
          current = current.next;
        }
        
         current.next = null;
        
        return reversedHead;        
    }