Singly vs Doubly Linked List
💡 Concept Name
Singly and Doubly Linked Lists – Linear data structures composed of nodes holding data and pointers for traversal.
📘 Quick Intro
A singly linked list connects nodes in one direction with a single pointer to the next node. A doubly linked list uses two pointers per node: one to the next node and another to the previous node, enabling bi-directional traversal.
🧠 Analogy / Short Story
A singly linked list is like a one-way street allowing travel only forward, while a doubly linked list resembles a two-way street enabling travel both forward and backward.
🔧 Technical Explanation
- 🔄 Singly Linked List: Each node contains data and a pointer to the next node.
- 🛂 Doubly Linked List: Each node contains data, a pointer to the next node, and a pointer to the previous node.
- ⏳ Traversal: Singly linked lists allow only forward traversal; doubly linked lists allow forward and backward traversal.
- ⚖️ Memory Usage: Doubly linked lists require more memory due to the additional pointer.
- ✅ Insertion & Deletion: Easier in doubly linked lists because of backward references.
🎯 Purpose & Use Case
- ✅ Singly linked lists are suitable for stacks, queues, and simple forward traversals.
- ✅ Doubly linked lists are preferred for navigation systems, such as browser history and undo-redo operations.
- ✅ Use doubly linked lists when bi-directional traversal or easier node removal is needed.
💻 Real Code Example
// Singly Linked List Node
public class SinglyNode {
public int Data;
public SinglyNode Next;
}
// Doubly Linked List Node
public class DoublyNode {
public int Data;
public DoublyNode Next;
public DoublyNode Prev;
}
❓ Interview Q&A
Q1: What is a singly linked list?
A: A linked list where each node points to the next node only.
Q2: What is a doubly linked list?
A: A linked list where each node points to both the next and the previous nodes.
Q3: What is the advantage of doubly linked lists over singly linked lists?
A: They allow traversal in both directions.
Q4: Which linked list uses more memory?
A: Doubly linked lists, because of the extra pointer for the previous node.
Q5: How does insertion differ between singly and doubly linked lists?
A: Doubly linked lists require updating two pointers, singly linked lists require one.
Q6: Can you traverse singly linked lists backward?
A: No, traversal is only forward.
Q7: Is deletion easier in doubly linked lists?
A: Yes, because you have direct access to the previous node.
Q8: What is the time complexity of search in both lists?
A: O(n) for both singly and doubly linked lists.
Q9: Are singly linked lists simpler to implement?
A: Yes, due to having only one pointer per node.
Q10: Which linked list is preferred for undo functionality?
A: Doubly linked lists, because they support backward traversal.
📝 MCQs
Q1. How many pointers does a node have in a singly linked list?
- None
- One (next)
- Two (next and previous)
- Three
Q2. How many pointers does a node have in a doubly linked list?
- One
- Two (next and previous)
- None
- Three
Q3. Which linked list allows backward traversal?
- Singly linked list
- Doubly linked list
- Both
- None
Q4. Which linked list uses more memory?
- Singly linked list
- Doubly linked list
- Both equal
- Depends on data
Q5. Is deletion easier in doubly linked lists?
- No
- Yes
- Sometimes
- Never
Q6. Can singly linked lists be traversed backward?
- Yes
- No
- Only with extra storage
- Sometimes
Q7. What is the time complexity of search in linked lists?
- O(1)
- O(n)
- O(log n)
- O(n log n)
Q8. Which linked list is simpler to implement?
- Singly linked list
- Doubly linked list
- Both equal
- Depends
Q9. Which linked list is better for undo operations?
- Singly linked list
- Doubly linked list
- Both
- None
Q10. How many pointers need updating during insertion in a doubly linked list?
- One
- Two
- Three
- None
💡 Bonus Insight
Circular doubly linked lists are commonly used in applications like music playlists where looping forward and backward continuously is desired.
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