//We are adding before the head to implement as a stack (Each new node added becomes the head)
//O(1) time complexity
public void Push(object x)
{
Node n = new Node(x);
n.Next = head;
this.head = n;
Count++;
}
//Worst case time complexity is O(n) if insertion is at end of list
//Passing a 1 for position adds object at head (it becomes first in the stack)
//passing the stack (count + 1) for position adds the inserted node at the end
//of the linked list stack, 0 is considered an invalid index
public void Insert(int position, object x)
{
if ((position < 1) || (position > Count + 1))
throw new IndexOutOfRangeException("Invalid index");
if (position == 1)
{
this.Push(x);
return;
}
//Set two pointer nodes to first and second position
Node lag = head;
Node lead = head.Next;
Node toInsert = new Node(x);
//Set the pointers to the nodes immediately before and after the inserted node
for (int i = 2; i < position; i++)
{
lag = lag.Next;
lead = lead.Next;
}
//Make the insertion
lag.Next = toInsert;
toInsert.Next = lead;
}
//Delete middle node in a linked list
//This method will delete any passed node except for the last node
//Attempting to delete the last node in this manner will not work
public void DeleteMiddle(Node x)
{
if (x.Next == null)
return;
//Copy data from next node to passed node
x.Data = x.Next.Data;
//Set Next pointer to node after copied data
x.Next = x.Next.Next;
}
//O(1) time complexity
public object Pop()
{
//This is how the C# Stack implementation in System.Collections handles popping an empty stack
if (head == null)
throw new InvalidOperationException("Stack empty");
object result = head.Data;
this.head = head.Next;
return result;
}
//Clears the Stack, resets the count
public void Clear()
{
head = null;
Count = 0;
}
public LinkedListStack()
{
head = null;
}
