Refactor Doubly Linked List implementation

DoublyLL.c

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