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https://github.com/Manoj-HV30/ds-lab-codes.git
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Refactor Doubly Linked List implementation
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GitHub
+136
-125
@@ -1,136 +1,147 @@
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#include <stdio.h>
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#include <stdlib.h>
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typedef struct element {
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int key;
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} element;
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typedef struct node *nodeptr;
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// Define the DLL Node
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struct Node {
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int data;
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struct Node *prev; // Pointer to previous node
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struct Node *next; // Pointer to next node
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};
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typedef struct node {
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nodeptr llink;
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element item;
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nodeptr rlink;
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} node;
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// Global Head Pointer
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struct Node *head = NULL;
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void insert(nodeptr head, int data);
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void delete(nodeptr head, nodeptr deleted);
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void display(nodeptr head);
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nodeptr search(nodeptr head, int key);
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// a) Insert a node (Create/Append) - 15 Marks
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// We insert at the END to simulate "Creating" a list naturally
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void insert(int value) {
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struct Node *temp;
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// 1. Allocate memory
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struct Node *newNode = (struct Node *)malloc(sizeof(struct Node));
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if (newNode == NULL) {
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printf("Memory allocation failed\n");
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return;
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}
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// 2. Set data
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newNode->data = value;
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newNode->next = NULL; // Since it will be the last node
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// 3. Case 1: List is Empty
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if (head == NULL) {
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newNode->prev = NULL; // First node has no prev
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head = newNode;
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printf("Node %d inserted as head.\n", value);
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return;
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}
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// 4. Case 2: List has data. Traverse to the end.
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temp = head;
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while (temp->next != NULL) {
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temp = temp->next;
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}
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// 5. Link the new node
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temp->next = newNode; // Old last node points to new node
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newNode->prev = temp; // New node points back to old last node
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printf("Node %d inserted at end.\n", value);
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}
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// b) Delete a node (by value) - 15 Marks
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void delete(int value) {
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struct Node *temp = head;
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// 1. Check if list is empty
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if (head == NULL) {
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printf("List is empty.\n");
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return;
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}
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// 2. Search for the node
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while (temp != NULL && temp->data != value) {
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temp = temp->next;
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}
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// 3. If node not found
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if (temp == NULL) {
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printf("Element %d not found.\n", value);
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return;
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}
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// --- Deletion Logic ---
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// Case A: Deleting the Head Node
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if (temp == head) {
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head = head->next; // Move head forward
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if (head != NULL) {
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head->prev = NULL; // New head's prev must be NULL
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}
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}
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// Case B: Deleting a Middle or Last Node
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else {
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// Link the previous node to the next node
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temp->prev->next = temp->next;
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// If there IS a next node (i.e., we are not deleting the last node),
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// Link the next node back to the previous node
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if (temp->next != NULL) {
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temp->next->prev = temp->prev;
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}
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}
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// 4. Free memory
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free(temp);
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printf("Node %d deleted.\n", value);
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}
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// c) Display the list - 5 Marks
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void display() {
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struct Node *temp = head;
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if (head == NULL) {
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printf("List is empty.\n");
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return;
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}
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printf("List (Forward): NULL <-> ");
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while (temp != NULL) {
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printf("%d <-> ", temp->data);
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temp = temp->next;
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}
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printf("NULL\n");
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}
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int main() {
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int choice, data;
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nodeptr node_to_delete;
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int choice, val;
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printf("--- Doubly Linked List Program ---\n");
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nodeptr head = (nodeptr)malloc(sizeof(node));
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if (head == NULL) {
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fprintf(stderr, "Memory allocation failed for head node.\n");
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exit(1);
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while (1) {
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printf("\n1. Insert (Create)\n2. Delete\n3. Display\n4. Exit\n");
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printf("Enter choice: ");
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scanf("%d", &choice);
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switch (choice) {
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case 1:
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printf("Enter value: ");
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scanf("%d", &val);
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insert(val);
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break;
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case 2:
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printf("Enter value to delete: ");
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scanf("%d", &val);
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delete(val);
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break;
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case 3:
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display();
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break;
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case 4:
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return 0;
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default:
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printf("Invalid Choice\n");
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}
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head->llink = head;
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head->rlink = head;
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while (1) {
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printf("\n--- Doubly Linked List Menu ---\n");
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printf("1. Insert (at front)\n");
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printf("2. Delete (by key)\n");
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printf("3. Display List\n");
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printf("4. Exit\n");
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printf("Enter your choice: ");
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scanf("%d", &choice);
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switch (choice) {
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case 1:
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printf("Enter number to insert: ");
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scanf("%d", &data);
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insert(head, data);
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printf("Item %d inserted.\n", data);
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break;
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case 2:
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printf("Enter number to delete: ");
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scanf("%d", &data);
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node_to_delete = search(head, data);
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if (node_to_delete == NULL) {
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printf("Item %d not found in the list.\n", data);
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} else {
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delete(head, node_to_delete);
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printf("Item %d deleted.\n", data);
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}
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break;
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case 3:
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display(head);
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break;
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case 4:
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printf("Exiting program.\n");
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free(head);
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exit(0);
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default:
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printf("Invalid choice. Please try again.\n");
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}
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}
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return 0;
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}
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return 0;
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}
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void insert(nodeptr head, int data) {
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nodeptr newnode = (nodeptr)malloc(sizeof(node));
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if (newnode == NULL) {
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fprintf(stderr, "Memory allocation failed for new node!\n");
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exit(1);
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}
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newnode->item.key = data;
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newnode->llink = head;
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newnode->rlink = head->rlink;
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head->rlink->llink = newnode;
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head->rlink = newnode;
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}
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void delete(nodeptr head, nodeptr deleted) {
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if (head == deleted) {
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printf("Deletion of the head node not permitted!\n");
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} else {
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deleted->llink->rlink = deleted->rlink;
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deleted->rlink->llink = deleted->llink;
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free(deleted);
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}
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}
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nodeptr search(nodeptr head, int key) {
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nodeptr temp = head->rlink;
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while (temp != head) {
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if (temp->item.key == key) {
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return temp;
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}
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temp = temp->rlink;
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}
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return NULL;
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}
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void display(nodeptr head) {
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nodeptr temp = head->rlink;
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if (temp == head) {
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printf("List is empty.\n");
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return;
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}
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printf("List: ");
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while (temp != head) {
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printf("%d ", temp->item.key);
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temp = temp->rlink;
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}
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printf("\n");
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}
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