How to Understand and Build a Singly Linked List

TL;DR

A linked list stores data in nodes that point to other nodes, allowing its size to change at runtime without requiring continuous memory. A singly linked list uses one next pointer per node, while a head pointer identifies the first node. Insertion at the head requires creating a node, connecting it to the current head, and updating the head.

Transcript

Hello ji, How are you all? this is Love Babbar Welcome to the channel Code help , today we are going to talk about linked list , this is lecture no-44 Here we will discuss all topics related to linked list After this there will be one more video where will solve many questions Lets understand what is a linked list? This is a type of linear data st... Read More

Key Insights

• A linked list is a linear data structure composed of nodes, and every demonstrated node contains both a data value and the address of the next node. The last node stores NULL in its next field because it does not point to another node.
• Linked-list nodes do not need continuous memory allocation, because pointers connect nodes stored at different locations. A head pointer identifies the first node, and following each node's next pointer provides a path through the entire list until NULL is reached.
• A linked list is dynamic because its size can increase or decrease while the program runs. The lecture presents this flexibility as an advantage over a fixed-size array, whose declared size cannot simply be changed from 10 elements to 100 during runtime.
• A vector expands by allocating new storage and copying its existing values after becoming fully filled. The lecture describes this copying and additional allocation as a cost, then introduces linked lists as a way to avoid that particular resizing process.
• Insertion and deletion in a linked list do not require shifting all later elements. The lecture contrasts this behavior with arrays, where inserting an element may require shifting values forward and deleting an element may require shifting values backward.
• A singly linked list gives each node one next pointer alongside its data. Other linked-list categories named in the lecture are doubly linked lists, circular linked lists, and circular doubly linked lists, although the demonstrated implementation focuses on the singly linked form.
• A node class can contain an integer named data and a Node pointer named next. Its constructor receives a data value, assigns that value to the node, and initializes next to NULL so a newly created node does not begin with an uninitialized pointer value.
• Insertion at the head requires three operations: create a temporary node containing the new data, set the temporary node's next pointer to the current head, and assign head to the temporary node. Passing head by reference allows the function to modify the original list.

Questions & Answers

Q: What is a linked list and how are its nodes connected?

A linked list is a linear data structure formed from a collection of nodes. Each node contains a data field and a pointer that stores the address of the next node. These pointers connect nodes even when they occupy separate memory locations. A head pointer identifies the first node, and the last node points to NULL to mark the end of the list.

Q: Why use a linked list instead of a fixed-size array?

A linked list can increase or decrease in size while the program is running, whereas the lecture's fixed-size array example cannot simply change from a size of 10 to a size of 100 at runtime. Linked lists also avoid requiring continuous memory locations. Their insertions and deletions can be performed without shifting all later elements forward or backward.

Q: How does a linked list differ from a dynamic array or vector?

The lecture explains that a vector is a dynamic array whose storage becomes larger when its existing space is completely filled. New storage is allocated, and the existing values are copied into it. A linked list instead adds separately allocated nodes and connects them through pointers, so it does not require the same continuous block or copying process when its size changes.

Q: What information does a singly linked-list node store?

A singly linked-list node stores two pieces of information: a data value and a pointer to the next node. In the demonstrated C++ class, the data field has the integer type, while the next field has the type Node pointer. Because there is one next pointer, each node directly identifies only the node that follows it in the list.

Q: How do you implement a linked-list node class in C++?

The demonstrated node class places an integer data field and a Node pointer named next in its public section. A constructor accepts an integer, assigns it to the current object's data field, and sets the current object's next field to NULL. A node can then be created dynamically with new Node and the desired data value as the constructor argument.

Q: How do you insert a new node at the head of a linked list?

First, create a temporary node with the data that must be inserted. Next, assign the current head pointer to the temporary node's next field, which connects the new node to the existing first node. Finally, assign the temporary node to head. The new node then becomes the first element, while the remainder of the list stays connected behind it.

Q: Why is the head pointer passed by reference during insertion?

The head pointer is passed by reference because insertion at the beginning must change the original pointer that identifies the first node. If the function worked only with a copied head pointer, assigning the new node to that copy would not update the original linked list outside the function. A reference allows the function's head assignment to persist after it returns.

Q: How do you traverse and print a singly linked list?

Create a temporary Node pointer and initialize it with head so the original head does not need to move. While the temporary pointer is not NULL, print the data stored in its current node and then update the temporary pointer to temp->next. Repeating these steps visits nodes in sequence and stops after the final node leads to NULL.

Summary & Key Takeaways

• A linked list is a linear data structure formed from a collection of nodes. Each node contains data and a pointer holding the address of the next node. The final node points to NULL, while a separate head pointer identifies the first node and provides access to the complete list.

• Unlike arrays, linked-list nodes do not require continuous memory locations. The structure can grow or shrink at runtime, and insertion or deletion does not require shifting neighboring elements. The lecture contrasts this behavior with vectors, which allocate new storage and copy existing values when their available capacity becomes completely filled.

• A singly linked-list node is implemented with a class containing an integer data field and a Node pointer named next. Its constructor assigns the supplied data and initializes next to NULL. The lecture then demonstrates head insertion and traversal using temporary pointers so that the original head can remain available.