Fix LinkedList.AddAtHead(), AddAtTail() methods

Author: Rion5

LeetCode/DataStructures/LinkedList.cs

@@ -9,61 +9,75 @@ public class Node
  // Fields
  public int? Data;
  public Node Next;
- public Node Previous;
 
  // Constructors
+ public Node()
+ {
+ this.Data = null;
+ this.Next = null;
+ }
  public Node(int value)
  {
  this.Data = value;
  this.Next = null;
- this.Previous = null;
  }
  }
 
  /// <summary>
  /// 707. Design Linked List
- /// Design your implemenation of the linked list. You can choose to use the singly linked list or the doubly lined list. A node in a singly linked list should have two attributes: val and next. Val is the value of the current node, next is a pointer/ reference to the next node. If you want to use the double linked list, you will need one more attribute prev to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.
+ /// Design your implementation of the linked list. You can choose to use the singly linked list or the doubly lined list. A node in a singly linked list should have two attributes: val and next. Val is the value of the current node, next is a pointer/ reference to the next node. If you want to use the double linked list, you will need one more attribute prev to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.
  /// </summary>
  public class LinkedList
  {
  private Node _head;
  private Node _tail;
 
- public int Count = 0;
+ public int Count;
 
  // Constructors
  public LinkedList()
  {
- this._head = null;
+ this._head = new Node();
  this._tail = null;
+ this.Count = 0;
  }
- public LinkedList(Node head)
+
+ //TODO: get(index), addAtIndex(index, val), deleteAtIndex(index)
+
+ /// <summary>
+ /// Append a node to the front of the linked list
+ /// </summary>
+ /// <param name="val"></param>
+ public void AddAtHead(int val)
  {
- this._head = head;
- if (head.Next == null)
+ // If LinkedList is empty, set both the head and tail to this node
+ // Else set the current list to the nodeToAdd'.Next and move the nodeToAdd to the front (head) of the LinkedList
+ Node nodeToAdd = new Node(val);
+ if (_head.Data == null)
  {
- Count = 1;
+ _head = nodeToAdd;
+ _tail = nodeToAdd;
  }
- while (head.Next != null)
+ else
  {
- this._tail = head.Next;
- Count++;
+ nodeToAdd.Next = _head;
+ _head = nodeToAdd;
  }
- }
-
- //TODO: get(index), addAtHead(val), addAtTail(val), addAtIndex(index, val), deleteAtIndex(index)
-
- public void AddAtHead(int val)
- {
-
+ Count++;
  }
 
  /// <summary>
- /// Append a node of values to the last element of the linked list.
+ /// Append a node the end of the linked list.
  /// </summary>
  /// <param name="val"></param>
  public void AddAtTail(int val)
  {
+ // If LinkedList is empty, add node to the head and exit out of function
+ if (_head.Data == null)
+ {
+ AddAtHead(val);
+ return;
+ }
  try
  {
  Node node = _head; // Set Node to first node in the list
@@ -83,21 +97,43 @@ public void AddAtTail(int val)
  public void AddAtIndex(int index, int val)
  {
 
+ if (index < 0) return;
+
+ // If LinkedList is empty, add node to the front
+ if (_head.Data == null)
+ {
+ AddAtHead(val);
+ return;
+ }
+
+ //If index is out of range of LinkedList, add node to the tail
+ if (index > Count)
+ {
+ AddAtTail(val);
+ return;
+ }
+
+ // Iterate to the index and insert
+
  }
 
  public void PrintLinkedList()
  {
+ Node node = _head;
+ if (node.Data == null && node.Next == null) return; //Check if LinkedList is null & empty
+
  Console.WriteLine($"707. Design Linked List");
  Console.WriteLine($"Print Linked List");
  Console.Write($"HEAD => ");
- Node node = _head;
- if (node.Data == null && node.Next == null) return; //Check if LinkedList is null & empty
+
+ // Iterate through each node, printing its value
  while (node.Data != null && node.Next != null)
  {
  Console.Write($"{node.Data} => ");
  node = node.Next;
  }
- 
+
+ // End of Linked List
  if (node.Next == null)
  {
  Console.Write($"{node.Data} => TAIL\n\n");