Singly linked list structure in Data Structures Theory - Step-by-Step Execution

Concept Flow - Singly linked list structure

Create new node

↓

Set node data and next pointer

↓

If list empty?

Yes→Set head to new node

↓

Traverse to last node

↓

Insert new node at end

↓

Done

This flow shows how a new node is created and added to a singly linked list, either as the first node or appended at the end.

Execution Sample

Data Structures Theory

head = None
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

new_node = Node(5)
if head is None:
    head = new_node
else:
    current = head
    while current.next:
        current = current.next
    current.next = new_node

This code creates a new node with data 5 and inserts it at the end of a singly linked list.

Analysis Table

Step	Operation	Nodes in List	Pointer Changes	Visual State
1	Start with empty list	None	head = None	head -> None
2	Create new node with data=5	Node(5)	new_node created	head -> None, new_node(5) -> None
3	Check if list empty	Node(5)	head is None (True)	head -> None
4	Set head to new_node	Node(5)	head = new_node	head -> Node(5) -> None
5	End of insertion	Node(5)	No pointer changes	head -> Node(5) -> None

💡 Insertion done because list was empty and head was set to new_node

State Tracker

Variable	Start	After Step 2	After Step 4	Final
head	None	None	Node(5)	Node(5)
new_node	None	Node(5)	Node(5)	Node(5)
current	None	None	None	None

Key Insights - 3 Insights

Why do we check if head is None before inserting?

Because if head is None, the list is empty and the new node becomes the first node (see execution_table step 3 and 4). Without this, we wouldn't know where to start inserting.

What does the 'next' pointer in a node represent?

It points to the next node in the list or None if it is the last node. This is shown in the Visual State column where Node(5) points to None.

Why don't we need to traverse the list when it is empty?

Because there are no nodes to traverse. The new node becomes the head immediately (execution_table step 3 and 4). Traversal happens only if the list is not empty.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what does the head pointer point to?

A The previous node

B None

C The new node with data 5

D An empty list

💡 Hint

Check the Pointer Changes and Visual State columns at step 4 in execution_table.

At which step does the list change from empty to having one node?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the Pointer Changes column where head is assigned to new_node.

If the list was not empty, what would happen instead of setting head to new_node?

A Delete the head node

B Traverse to last node and set its next to new_node

C Set head to None

D Do nothing

💡 Hint

Refer to the concept_flow where the 'No' branch leads to traversal and insertion at the end.

Concept Snapshot

Singly linked list stores nodes where each node points to the next.
Head points to the first node or None if empty.
To insert, create a new node.
If empty, set head to new node.
Else, traverse to last node and link new node.
Each node's 'next' points to the following node or None.

Full Transcript

A singly linked list is a chain of nodes where each node holds data and a pointer to the next node. The list starts with a head pointer. When inserting a new node, if the list is empty (head is None), the new node becomes the head. Otherwise, we traverse the list to find the last node and set its next pointer to the new node. This process ensures nodes are linked in order. The 'next' pointer of the last node is always None, marking the list's end.