/// <summary>
/// Prints the contents of a list in reverse
/// </summary>
/// <remarks>
/// This approach uses a stack to push and pop off the values.
/// </remarks>
/// <param name="node"></param>
public static void RunIterativelyReverse(LinkListNode node)
{
Stack<LinkListNode> stack = new Stack<LinkListNode>();
// Step #1 - push all the elements into a stack
for (LinkListNode n = node; n != null; n = n.next)
{
stack.Push(n); // PUSH
}
Console.Write("(null)");
// Step #2 - pop each element off and print
while (stack.Count != 0)
{
stack.Pop().PrintNode(false, false); // POP
if (node.prev != null)
{
Console.Write("<->");
}
else
{
if (stack.Count > 0)
{
Console.Write("<-");
}
}
}
}
/// <summary>
/// Determines if linked list contains a loop
/// Method: Use two pointers to traverse the list, one slow (increments by 1) and one fast (increments by 2)
/// If the faster pointer reaches null, the linked list does not contain a loop.
/// If the slower pointer is ahead of the faster pointer or equal to it, then a loop is present.
/// Performance: Leading pointer ends at n nodes, trailing pointer would have reached n/2
/// 3/2n = O(n) 1 1/2 nodes examined
/// </summary>
/// <param name="head"></param>
/// <returns></returns>
public static bool Run( LinkListNode head)
{
if (head == null)
{
throw new System.ArgumentNullException("FindLoopInList error, arguement head cannot be null.");
}
LinkListNode leadingPtr;
LinkListNode trailingPtr;
trailingPtr = head;
leadingPtr = trailingPtr.next;
if (leadingPtr == null) return false;
while (leadingPtr != null && trailingPtr != null)
{
if (trailingPtr == leadingPtr)
{
return true;
}
trailingPtr = trailingPtr.next;
leadingPtr = leadingPtr.next;
if (leadingPtr != null)
{
leadingPtr = leadingPtr.next;
}
else
{
return false;
}
}
return false;
}
/// <summary>
/// Finds the nth to last element in a linked list
/// </summary>
/// <remarks>
/// This approach uses a leading and trailing pointer to step through the link list
/// The leading pointer is sent out first and a counter is kept.
/// Once the counter reaches the nth mark, the trailing pointer is advanced
/// When the leading pointer reaches null, the trailing pointer will be pointing at the nth element.
///
/// </remarks>
/// <returns></returns>
public static int RunIterative(LinkListNode head, int nth)
{
LinkListNode leadingPtr;
LinkListNode trailingPtr;
if (head == null)
{
throw new System.ArgumentNullException("FindNthToLast, head must be a non null value.");
}
leadingPtr = head;
for (int i=0; i<nth; i++)
{
leadingPtr = leadingPtr.next;
if (leadingPtr == null)
{
throw new System.ArgumentOutOfRangeException("FindNthToLast, nth is out of range");
}
}
trailingPtr = head;
while (leadingPtr.next != null)
{
trailingPtr = trailingPtr.next;
leadingPtr = leadingPtr.next;
}
return trailingPtr.key;
}
/// <summary>
/// Adds the values of all the nodes in a linked list using recusion
/// </summary>
/// <remarks>
/// Recursion terminates when we reach null.
/// Add the node value to the return value and call next node.
/// </remarks>
/// <param name="head"></param>
/// <returns></returns>
public static int RunRecusively(LinkListNode head)
{
if (head == null)
{
return 0;
}
else
{
return head.key + RunRecusively(head.next);
}
}
/// <summary>
/// Finds the length of a linked list recursively
/// </summary>
/// <remarks>
/// Recursive operation terminates when we reach null node.
/// We add one to the returned value and pass in next node.
/// </remarks>
/// <returns></returns>
public static int RunRecursively(LinkListNode head)
{
if (head == null) // terminate logic when we reach end of linked list
{
return 0;
}
else
{
return 1 + RunRecursively(head.next); // simply add 1 and call until we reach end of list
}
}
/// <summary>
/// Finds the nth to last element in a linked list
/// </summary>
/// <param name="head"></param>
/// <param name="nth"></param>
/// <returns></returns>
public static void RunRecursion(LinkListNode head, int nth)
{
if (head == null)
{
return;
}
RunRecursion(head.next, nth);
if (i++ == nth)
{
Console.WriteLine(nth.ToString() + " to last element in linked list: " + head.key);
}
}
/// <summary>
/// Reverses a linked list
/// </summary>
/// <remarks>
///
/// Steps:
/// If we reach null, pass back node (recursive termination condition)
/// Get next node, by recusively calling function and passing node's next
/// Switch pointer, point heads.next's next pointer back at head
/// Break head's next link, set next to null
/// return the node
///
/// </remarks>
/// <param name="head"></param>
/// <returns></returns>
public static LinkListNode RunRecursively(LinkListNode head)
{
LinkListNode node;
if (head.next == null)
{
return head; // recursive termination condition
}
node = RunRecursively(head.next); // dive down into the linked list
head.next.next = head; // point head's next node's next pointer back at head
head.next = null; // break link from head to next node
return node; // return node
}
/// <summary>
/// Removes a node from a linked list
/// </summary>
/// <remarks>
/// Note this approach only works when removing nodes other than head
/// </remarks>
/// <param name="node"></param>
/// <param name="key"></param>
/// <returns></returns>
public static LinkListNode RunRecursively(LinkListNode node, int key)
{
if (node != null)
{
if (node.key == key)
{
node = node.next; // advance the pointer
}
else
{
node.next = RunRecursively(node.next, key);
}
}
return node;
}
/// <summary>
/// Reverses a linked list
/// </summary>
/// <remarks>
/// This uses an iterative approach using a current, previous and next pointer.
///
/// Steps:
/// Get handle to next node, assign next to point to next node
/// Break link to next node, assign current's next to previous
/// No longer need previous, reassign previous to current
/// Advance current to next
/// Repeat until current is null
/// </remarks>
/// <param name="head"></param>
/// <returns></returns>
public static void RunIteratively(ref LinkListNode head)
{
LinkListNode current = head;
LinkListNode previous = null;
LinkListNode next = null;
while (current != null)
{
next = current.next; // step the next pointer by one
current.next = previous; // reassign current node to point to previous
previous = current; // advance previous to the current node
current = next; // increment current to the next node
}
head = previous;
}
/// <summary>
/// Creates a copy of a linked list
/// </summary>
/// <remarks>
/// Uses a rescursive approach to copy each element of a linked list
/// </remarks>
/// <param name="head"></param>
/// <returns></returns>
public static LinkListNode RunRecursively(LinkListNode head)
{
LinkListNode node;
if (head == null)
{
return null;
}
else
{
node = new LinkListNode();
node.key = head.key;
node.next = RunRecursively(head.next);
return node;
}
}
/// <summary>
/// Removes a node from a ordered linked list
/// </summary>
/// <param name="head"></param>
/// <param name="key"></param>
/// <param name="isDoublyLinked"></param>
public static void Run(ref LinkListNode head, int key, bool isDoublyLinked)
{
LinkListNode node;
LinkListNode prev;
if (head == null)
{
throw new System.ArgumentNullException("RemoveNode Error, head cannont be a null value.");
}
//Check #1 - Check if we are removing head
if (head.key == key)
{
node = head;
head = head.next;
if (isDoublyLinked == true && head != null)
{
head.prev = null;
}
node = null;
}
else
{
node = null;
prev = head;
while (prev.next != null && prev.next.key != key)
{
prev = prev.next;
}
if (prev.next != null && prev.next.key == key)
{
node = prev.next;
prev.next = node.next;
if (isDoublyLinked == true && node.next != null)
{
node.next.prev = node;
}
node = null;
}
else
{
Console.WriteLine("RemoveNode Warning - value " + key + " was not found in linked list.");
}
}
}
/// <summary>
/// Creates a singly linked list
/// </summary>
/// <param name="values"></param>
/// <param name="head"></param>
public static void CreateSinglyLinked(int[] values, out LinkListNode head)
{
LinkListNode node = null;
if (values == null || values.Length == 0)
{
throw new System.ArgumentException("CreateList error, values must contain at least one value.");
}
head = new LinkListNode();
head.key = values[0];
node = head;
for (int i = 1; i < values.Length; i++)
{
node.next = new LinkListNode(); // assign the next pointer of current node
node = node.next; // advance pointer to newly created node
node.key = values[i]; // assign value to new node from passed in arguments
}
}
/// <summary>
/// Finds the length of a linked list iteratively
/// </summary>
/// <returns></returns>
public static int RunIteratively(LinkListNode head)
{
LinkListNode node;
int i;
if (head == null)
{
return 0;
}
node = head;
i = 1;
while (node.next != null)
{
node = node.next;
i++;
}
node = null;
return i;
}
/// <summary>
/// Iteratively adds the node values in a linked list
/// </summary>
/// <param name="head"></param>
/// <returns></returns>
public static int RunIteratively(LinkListNode head)
{
LinkListNode node;
int sum;
if (head == null)
{
return 0;
}
node = head;
sum = head.key;
while (node.next != null)
{
node = node.next;
sum += node.key;
}
node = null;
return sum;
}
/// <summary>
/// Prints the contents of a linked list
/// </summary>
/// <param name="head"></param>
public static void RunIteratively(LinkListNode head)
{
LinkListNode node;
if (head == null)
{
throw new System.ArgumentNullException("PrintList error, head arguement null.");
}
node = head;
// check for loop
if (FindLoopInList.Run(head) == true)
{
Console.WriteLine("PrintList Warning, list contains loop, unable to print.");
return;
}
while (node != null)
{
node.PrintNode(false, false);
if (node.prev != null && node.next != null)
{
Console.Write("<->");
}
else
{
Console.Write("->");
}
node = node.next;
if (node == null)
{
Console.Write("(null)\n");
}
}
}
/// <summary>
/// Prints the contents of a linked list
/// </summary>
/// <remarks>
/// Recursively traverses the linked list and prints out node values
/// </remarks>
/// <param name="node"></param>
public static void RunRecursively(LinkListNode node)
{
if (node == null)
{
Console.Write("(null)\n");
return;
}
else
{
node.PrintNode(false, false);
if (node.prev != null && node.next != null)
{
Console.Write("<->");
}
else
{
Console.Write("->");
}
RunRecursively(node.next);
}
}
/// <summary>
/// Prints the contents of a linked list in reverse
/// </summary>
/// <param name="node"></param>
public static void RunRecursivelyReverse(LinkListNode node)
{
if (node == null)
{
Console.Write("(null)"); // <- Note the order, very important!!!
return;
}
else
{
RunRecursivelyReverse(node.next); // <- Note the order, very important!!!
if (node.next != null) // we check for "next" instead of "prev"
{
Console.Write("<->");
}
else
{
Console.Write("<-"); // we write arrow before writting number
}
node.PrintNode(false, false);
}
}
/// <summary>
/// Finds the location to insert the node
/// </summary>
/// <param name="head"></param>
/// <param name="key"></param>
/// <returns></returns>
private static LinkListNode FindPosition(LinkListNode head, int key)
{
LinkListNode prev = null;
if (head.key > key)
{
return null; // return null;
}
else
{
prev = head;
while (prev.next != null && key > prev.next.key)
{
prev = prev.next;
}
}
return prev;
}
/// <summary>
/// Inserts value into linked list
/// </summary>
/// <param name="head"></param>
/// <param name="key"></param>
/// <param name="isDoublyLinked"></param>
public static void Run( LinkListNode head, int key, bool isDoublyLinked = false)
{
LinkListNode node;
LinkListNode prev;
node = new LinkListNode();
node.key = key;
// Check #1 - Insert as new head if no head exists
if (head == null)
{
node.next = null;
node.prev = null;
head = node;
return;
}
// Check #2 - Insert as new head
if (head.key > key)
{
// Option 1, use "ref" keyword and change what head points to.
node.prev = null;
node.next = head;
if (isDoublyLinked == true)
{
head.prev = node;
}
head = node;
/*
// Option 2, insert new node after head and swap head and new node's key, retaining heads reference
node.next = head.next;
head.next = node;
node.key = head.key;
head.key = key;
if (isDoublyLinked == true)
{
if(node.next != null)
{
node.next.prev = node;
}
node.prev = head;
}
**/
}
else
{
prev = head;
while (prev.next != null && key > prev.next.key)
{
prev = prev.next;
}
node.next = prev.next;
prev.next = node;
if (isDoublyLinked == true)
{
if (node.next != null)
{
node.next.prev = node;
}
node.prev = head;
}
}
}
