Linked Lists Explained

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Questions and Answers

What distinguishes a doubly linked list from a singly linked list?

  • Doubly linked lists can only store integer data, while singly linked lists can store any data type.
  • Doubly linked lists have nodes containing a pointer to the next and previous nodes, allowing traversal in both directions, while singly linked lists only have a pointer to the next node. (correct)
  • Singly linked lists have a tail pointer, enabling O(1) insertion at the end, whereas doubly linked lists do not.
  • Doubly linked lists are circular, whereas singly linked lists always terminate with a NULL pointer.

In a singly linked list, what is the time complexity to insert a node at the end, assuming you only have a pointer to the head?

  • O(n^2)
  • O(1)
  • O(log n)
  • O(n) (correct)

Which of the following scenarios benefits most from using a circular linked list?

  • Managing a playlist that loops back to the beginning after the last song. (correct)
  • Implementing a binary search tree.
  • Implementing a LIFO stack data structure.
  • Storing a sorted list of unique elements.

Consider a singly linked list. What is the time complexity of deleting a node given a pointer to that node?

<p>O(n) (C)</p> Signup and view all the answers

Which of the following is NOT an advantage of using linked lists over arrays?

<p>Direct access to elements using an index. (A)</p> Signup and view all the answers

What is the purpose of the following code snippet in the context of linked lists?

NODE *current = head;
while (current != NULL) {
    current = current->next;
}

<p>To traverse the linked list from head to tail. (B)</p> Signup and view all the answers

In the provided delete_node function, what is the purpose of the prev pointer?

<p>To maintain a reference to the node preceding the one being deleted, allowing for proper unlinking in a singly linked list. (B)</p> Signup and view all the answers

What is the primary reason the insert_beginning function takes a NODE **head (pointer to a pointer) as an argument rather than NODE *head?

<p>To allow the function to modify the head of the linked list directly. (A)</p> Signup and view all the answers

If you need to frequently insert and delete nodes at arbitrary positions within a list, which type of linked list would generally be more suitable?

<p>Doubly linked list (A)</p> Signup and view all the answers

In a circular singly linked list, what condition is used to determine when to stop traversing the list?

<p>When the current node's <code>next</code> pointer points back to the head of the list. (D)</p> Signup and view all the answers

Which of the following scenarios would be best suited for using a singly linked list rather than a doubly linked list?

<p>A situation where memory usage is highly constrained and backward traversal is not needed. (D)</p> Signup and view all the answers

In terms of memory usage, how does a doubly linked list compare to a singly linked list with the same number of nodes?

<p>Doubly linked list uses more memory. (C)</p> Signup and view all the answers

What potential issue should be considered when deleting a node in a linked list?

<p>Memory leak if the deleted node's memory is not freed. (C)</p> Signup and view all the answers

Why is searching for an element in a linked list generally an O(n) operation?

<p>Linked list elements are not stored in contiguous memory locations, requiring sequential traversal. (A)</p> Signup and view all the answers

Consider a scenario where you need to implement a queue. Which type of linked list would simplify the implementation of enqueue (add to the end) in O(1) time?

<p>Singly linked list with both head and tail pointers. (D)</p> Signup and view all the answers

In the given delete_node function, what happens if the key (data value) to be deleted is not found in the linked list?

<p>The function does nothing and the linked list remains unchanged. (A)</p> Signup and view all the answers

What is the primary benefit of using linked lists for dynamic memory allocation compared to static arrays?

<p>Linked lists can grow or shrink during runtime as needed, whereas static arrays have a fixed size. (C)</p> Signup and view all the answers

For a very large linked list, which operation would likely be faster if the list was implemented as a doubly linked list instead of a singly linked list?

<p>Deleting a node given a pointer to the node to be deleted. (C)</p> Signup and view all the answers

A program uses a linked list to store data. During execution, the program's memory usage unexpectedly increases. What is a likely cause if nodes are being created and deleted?

<p>Deleted nodes are not having their memory deallocated, leading to a memory leak. (D)</p> Signup and view all the answers

Suppose you have to merge two sorted singly linked lists into one sorted linked list. What would be an efficient approach?

<p>Use a recursive function that compares the heads of both lists and builds the merged list incrementally. (D)</p> Signup and view all the answers

Flashcards

Singly Linked List

Each node contains data and a pointer to the next node, allowing traversal in one direction only.

Doubly Linked List

Each node contains data, a pointer to the next node, and a pointer to the previous node, enabling traversal in both directions.

Circular Linked List

The last node points back to the first node, forming a loop.

Insertion at Beginning

Adding a node at the beginning of the list.

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Insertion at End

Adding a node at the end of the list. Requires traversing the list if only the head pointer is available.

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Deletion From Beginning

Removing the first node from the list.

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Deletion From End

Removing a node from the end of the list, requires traversing the list to find the second-to-last element.

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Search in Linked List

Locating a specific element within the linked list.

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Head Pointer

A pointer that stores the address of the first node in a linked list.

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Inserting at Beginning Code

Insert a new node by allocating memory, assigning data, and linking it to the current head; then update the head.

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Deleting a Node Code

Removing a node involves finding it, unlinking it from the list by updating the previous node's next pointer, and freeing the memory.

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Study Notes

  • Linked lists are a data structure where elements are stored in nodes.
  • Each node contains data and a pointer to the next node.

Singly Linked List

  • Each node contains data and a pointer to the next node.
  • Traversal is possible in only one direction.
  • The head pointer tracks the first node in the list.

Doubly Linked List

  • Each node stores data, a pointer to the next node, and a pointer to the previous node.
  • Traversal is possible in both directions.
  • Requires more memory compared to singly linked lists.
  • Some operations are easier to implement due to the ability to traverse backwards.

Circular Linked List

  • The last node points back to the first node.
  • Can be either singly or doubly linked.

Insertion Operations

  • At the beginning: O(1)
  • At the end: O(n) with just the head pointer, or O(1) with a tail pointer
  • In the middle (after a given node): O(1)
  • In the middle (at a given position): O(n)

Deletion Operations

  • From the beginning: O(1)
  • From the end: O(n) with just the head pointer
  • From the middle (given node): O(1) if doubly linked, O(n) if singly linked

Search Operation

  • O(n), because it is necessary to traverse from the beginning

Common Code Patterns for Linked Lists

  • Traversing a linked list involves starting at the head and following the next pointers until the end of the list is reached
NODE *current = head;
while (current != NULL) {
    // Process current node
    current = current->next;
}
  • Inserting a node at the beginning of a linked list requires updating the head pointer
void insert_beginning(NODE **head, int data) {
    NODE *new_node = (NODE *)malloc(sizeof(NODE));
    new_node->data = data;
    new_node->next = *head;
- head = new_node;
}
  • Deleting a node involves finding the node and updating the next pointer of the previous node.
void delete_node(NODE **head, int key) {
    NODE *temp = *head, *prev = NULL;
    
    // If head node itself holds the key
    if (temp != NULL && temp->data == key) {
- head = temp->next;
        free(temp);
        return;
    }
    
    // Search for the key
    while (temp != NULL && temp->data != key) {
        prev = temp;
        temp = temp->next;
    }
    
    // If key not found
    if (temp == NULL) return;
    
    // Unlink node from list
    prev->next = temp->next;
    free(temp);
}

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