feat: add Circular Doubly Linked List implementation (#1038)

* Create circular_doubly_linked_list.c

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update circular_doubly_linked_list.c

Added brief description of library files

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update circular_doubly_linked_list.c

Done the all suggested changes.

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update circular_doubly_linked_list.c

* updating DIRECTORY.md

* updating DIRECTORY.md

* updating DIRECTORY.md

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* There was typo while calling delete_first_node !

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: David Leal <halfpacho@gmail.com>

* updating DIRECTORY.md

* Suggested changes are done.

Done the suggested changes in functions 
1. delete_first_node() 
2. delete_last_node()

* updating DIRECTORY.md

* updating DIRECTORY.md

* Worked on Suggested Changes

* Suggested changes are done.

* Update circular_doubly_linked_list.c

Worked on all the suggested changes.

Co-Authored-By: David Leal <halfpacho@gmail.com>
Co-Authored-By: CascadingCascade <122662061+CascadingCascade@users.noreply.github.com>
Co-Authored-By: Taj <tjgurwara99@users.noreply.github.com>

* updating DIRECTORY.md

* updating DIRECTORY.md

* Worked on suggested changes for test cases.

Check the code's functionality [here](https://leetcode.com/playground/WcRBMWa8)

Co-Authored-By: CascadingCascade <122662061+CascadingCascade@users.noreply.github.com>

* updating DIRECTORY.md

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: CascadingCascade <122662061+CascadingCascade@users.noreply.github.com>

* Update circular_doubly_linked_list.c

Update: Worked on suggested changes.

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: CascadingCascade <122662061+CascadingCascade@users.noreply.github.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: CascadingCascade <122662061+CascadingCascade@users.noreply.github.com>

* Update data_structures/linked_list/circular_doubly_linked_list.c

Co-authored-by: CascadingCascade <122662061+CascadingCascade@users.noreply.github.com>

* Worked on suggested changes.

* Minor upgrade.

* updating DIRECTORY.md

---------

Co-authored-by: David Leal <halfpacho@gmail.com>
Co-authored-by: github-actions[bot] <github-actions@users.noreply.github.com>
Co-authored-by: CascadingCascade <122662061+CascadingCascade@users.noreply.github.com>
Co-authored-by: Taj <tjgurwara99@users.noreply.github.com>

DIRECTORY.md

@@ -86,6 +86,7 @@
     * [Min Heap](https://github.com/TheAlgorithms/C/blob/HEAD/data_structures/heap/min_heap.c)
   * Linked List
     * [Ascending Priority Queue](https://github.com/TheAlgorithms/C/blob/HEAD/data_structures/linked_list/ascending_priority_queue.c)
+    * [Circular Doubly Linked List](https://github.com/TheAlgorithms/C/blob/HEAD/data_structures/linked_list/circular_doubly_linked_list.c)
     * [Circular Linked List](https://github.com/TheAlgorithms/C/blob/HEAD/data_structures/linked_list/circular_linked_list.c)
     * [Doubly Linked List](https://github.com/TheAlgorithms/C/blob/HEAD/data_structures/linked_list/doubly_linked_list.c)
     * [Merge Linked Lists](https://github.com/TheAlgorithms/C/blob/HEAD/data_structures/linked_list/merge_linked_lists.c)

data_structures/linked_list/circular_doubly_linked_list.c

@@ -0,0 +1,304 @@
+/**
+ * @file
+ *
+ * @details
+ * Circular [Doubly Linked
+ * List](https://en.wikipedia.org/wiki/Doubly_linked_list) combines the
+ * properties of a doubly linked list and a circular linked list in which two
+ * consecutive elements are linked or connected by the previous. Next, the
+ * pointer and the last node point to the first node via the next pointer, and
+ * the first node points to the last node via the previous pointer.
+ *
+ * In this implementation, functions to insert at the head, insert at the last
+ * index, delete the first node, delete the last node, display list, and get
+ * list size functions are coded.
+ *
+ * @author [Sahil Kandhare](https://github.com/SahilK-027)
+ *
+ */
+
+#include <assert.h>  /// to verify assumptions made by the program and print a diagnostic message if this assumption is false.
+#include <inttypes.h>  /// to provide a set of integer types with universally consistent definitions that are operating system-independent
+#include <stdio.h>     /// for IO operations
+#include <stdlib.h>  /// for including functions involving memory allocation such as `malloc`
+
+/**
+ * @brief Circular Doubly linked list struct
+ */
+typedef struct node
+{
+    struct node *prev, *next;  ///< List pointers
+    uint64_t value;            ///< Data stored on each node
+} ListNode;
+
+/**
+ * @brief Create a list node
+ * @param data                  the data that the node initialises with
+ * @return ListNode*            pointer to the newly created list node
+ */
+ListNode *create_node(uint64_t data)
+{
+    ListNode *new_list = (ListNode *)malloc(sizeof(ListNode));
+    new_list->value = data;
+    new_list->next = new_list;
+    new_list->prev = new_list;
+    return new_list;
+}
+
+/**
+ * @brief Insert a node at start of list
+ * @param head                  start pointer of list
+ * @param data                  the data that the node initialises with
+ * @return ListNode*            pointer to the newly created list node
+ * inserted at the head
+ */
+ListNode *insert_at_head(ListNode *head, uint64_t data)
+{
+    if (head == NULL)
+    {
+        head = create_node(data);
+        return head;
+    }
+    else
+    {
+        ListNode *temp;
+        ListNode *new_node = create_node(data);
+        temp = head->prev;
+        new_node->next = head;
+        head->prev = new_node;
+        new_node->prev = temp;
+        temp->next = new_node;
+        head = new_node;
+        return head;
+    }
+}
+
+/**
+ * @brief Insert a node at end of list
+ *
+ * @param head                  start pointer of list
+ * @param data                  the data that the node initialises with
+ * @return ListNode*            pointer to the newly added list node that was
+ * inserted at the head of list.
+ */
+ListNode *insert_at_tail(ListNode *head, uint64_t data)
+{
+    if (head == NULL)
+    {
+        head = create_node(data);
+        return head;
+    }
+    else
+    {
+        ListNode *temp1, *temp2;
+        ListNode *new_node = create_node(data);
+        temp1 = head;
+        temp2 = head->prev;
+        new_node->prev = temp2;
+        new_node->next = temp1;
+        temp1->prev = new_node;
+        temp2->next = new_node;
+        return head;
+    }
+}
+
+/**
+ * @brief  Function for deletion of the first node in list
+ *
+ * @param head              start pointer of list
+ * @return ListNode*        pointer to the list node after deleting first node
+ */
+ListNode *delete_from_head(ListNode *head)
+{
+    if (head == NULL)
+    {
+        printf("The list is empty\n");
+        return head;
+    }
+    ListNode *temp1, *temp2;
+    temp1 = head;
+    temp2 = temp1->prev;
+    if (temp1 == temp2)
+    {
+        free(temp2);
+        head = NULL;
+        return head;
+    }
+    temp2->next = temp1->next;
+    (temp1->next)->prev = temp2;
+    head = temp1->next;
+    free(temp1);
+    return head;
+}
+
+/**
+ * @brief Function for deletion of the last node in list
+ *
+ * @param head              start pointer of list
+ * @return ListNode*        pointer to the list node after deleting first node
+ */
+ListNode *delete_from_tail(ListNode *head)
+{
+    if (head == NULL)
+    {
+        printf("The list is empty\n");
+        return head;
+    }
+
+    ListNode *temp1, *temp2;
+    temp1 = head;
+    temp2 = temp1->prev;
+    if (temp1 == temp2)
+    {
+        free(temp2);
+        head = NULL;
+        return head;
+    }
+    (temp2->prev)->next = temp1;
+    temp1->prev = temp2->prev;
+    free(temp2);
+    return head;
+}
+
+/**
+ * @brief The function that will return current size of list
+ *
+ * @param head      start pointer of list
+ * @return int      size of list
+ */
+int getsize(ListNode *head)
+{
+    if (!head)
+    {
+        return 0;
+    }
+    int size = 1;
+    ListNode *temp = head->next;
+    while (temp != head)
+    {
+        temp = temp->next;
+        size++;
+    }
+    return size;
+}
+
+/**
+ * @brief   Display list function
+ * @param   head   start pointer of list
+ * @returns void
+ */
+
+void display_list(ListNode *head)
+{
+    printf("\nContents of your linked list: ");
+    ListNode *temp;
+    temp = head;
+    if (head != NULL)
+    {
+        while (temp->next != head)
+        {
+            printf("%" PRIu64 " <-> ", temp->value);
+            temp = temp->next;
+        }
+        if (temp->next == head)
+        {
+            printf("%" PRIu64, temp->value);
+        }
+    }
+    else
+    {
+        printf("The list is empty");
+    }
+    printf("\n");
+}
+
+/**
+ * @brief access the list by index
+ * @param list pointer to the target list
+ * @param index access location
+ * @returns the value at the specified index,
+ *          wrapping around if the index is larger than the size of the target
+ * list
+ */
+uint64_t get(ListNode *list, const int index)
+{
+    if (list == NULL || index < 0)
+    {
+        exit(EXIT_FAILURE);
+    }
+    ListNode *temp = list;
+    for (int i = 0; i < index; ++i)
+    {
+        temp = temp->next;
+    }
+    return temp->value;
+}
+
+/**
+ * @brief Self-test implementations
+ * @returns void
+ */
+static void test()
+{
+    ListNode *testList = NULL;
+    unsigned int array[] = {2, 3, 4, 5, 6};
+
+    assert(getsize(testList) == 0);
+
+    printf("Testing inserting elements:\n");
+    for (int i = 0; i < 5; ++i)
+    {
+        display_list(testList);
+        testList = insert_at_head(testList, array[i]);
+        assert(testList->value == array[i]);
+        assert(getsize(testList) == i + 1);
+    }
+
+    printf("\nTesting removing elements:\n");
+    for (int i = 4; i > -1; --i)
+    {
+        display_list(testList);
+        assert(testList->value == array[i]);
+        testList = delete_from_head(testList);
+        assert(getsize(testList) == i);
+    }
+
+    printf("\nTesting inserting at tail:\n");
+    for (int i = 0; i < 5; ++i)
+    {
+        display_list(testList);
+        testList = insert_at_tail(testList, array[i]);
+        assert(get(testList, i) == array[i]);
+        assert(getsize(testList) == i + 1);
+    }
+
+    printf("\nTesting removing from tail:\n");
+    for (int i = 4; i > -1; --i)
+    {
+        display_list(testList);
+        testList = delete_from_tail(testList);
+        assert(getsize(testList) == i);
+        // If list is not empty, assert that accessing the just removed element
+        // will wrap around to the list head
+        if (testList != NULL)
+        {
+            assert(get(testList, i) == testList->value);
+        }
+        else
+        {
+            // If the list is empty, assert that the elements were removed after
+            // the correct number of iterations
+            assert(i == 0);
+        }
+    }
+}
+
+/**
+ * @brief Main function
+ * @returns 0 on exit
+ */
+int main()
+{
+    test();  // run self-test implementations
+    return 0;
+}