Traversal and Printing a Linked List in DSA Python - Execution Trace

Concept Flow - Traversal and Printing a Linked List

Start at head node

↓

Is current node None?

Yes→Stop traversal

No↓

Print current node data

↓

Move to next node

↩Back to check current node

Start from the first node, print its data, move to the next node, repeat until no nodes left.

Execution Sample

DSA Python

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

current = head
while current:
    print(current.data)
    current = current.next

This code prints all data values in the linked list by moving from head to the end.

Execution Table

Step	Operation	Nodes in List	Pointer Changes	Visual State
1	Start at head	1 -> 2 -> 3 -> None	current = head (Node 1)	current -> 1 -> 2 -> 3 -> None
2	Print current.data	1 -> 2 -> 3 -> None	No change	Print: 1 current -> 1 -> 2 -> 3 -> None
3	Move to next node	1 -> 2 -> 3 -> None	current = current.next (Node 2)	current -> 2 -> 3 -> None
4	Print current.data	1 -> 2 -> 3 -> None	No change	Print: 2 current -> 2 -> 3 -> None
5	Move to next node	1 -> 2 -> 3 -> None	current = current.next (Node 3)	current -> 3 -> None
6	Print current.data	1 -> 2 -> 3 -> None	No change	Print: 3 current -> 3 -> None
7	Move to next node	1 -> 2 -> 3 -> None	current = current.next (None)	current -> None
8	Check current is None	1 -> 2 -> 3 -> None	No change	Traversal ends

💡 current becomes None, traversal stops

Variable Tracker

Variable	Start	After Step 1	After Step 3	After Step 5	After Step 7	Final
current	head (Node 1)	Node 1	Node 2	Node 3	None	None

Key Moments - 3 Insights

Why do we check if current is None before printing?

Because when current is None, it means we reached the end of the list and there is no data to print. See step 8 in execution_table where traversal stops.

Why do we move current to current.next after printing?

To go to the next node in the list. If we don't move, we would print the same node repeatedly. See steps 3, 5, and 7 where current moves forward.

What happens if the list is empty (head is None)?

The loop never runs because current starts as None. So nothing is printed and traversal ends immediately, like step 8 but from the start.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of current after step 5?

A None

B Node 2

C Node 3

D Node 1

💡 Hint

Check the 'Pointer Changes' column at step 5 in execution_table.

At which step does the traversal stop because current becomes None?

A Step 6

B Step 8

C Step 7

D Step 5

💡 Hint

Look at the 'Operation' and 'Visual State' columns in execution_table for when current is None.

If the linked list had only one node, how many times would the print operation run?

A 1 time

B 0 times

C 2 times

D 3 times

💡 Hint

Refer to variable_tracker and execution_table to see how many nodes are printed.

Concept Snapshot

Traversal and Printing a Linked List:
- Start at head node
- While current node is not None:
  - Print current node's data
  - Move to next node
- Stop when current is None
This prints all nodes in order.

Full Transcript

Traversal and printing a linked list means starting at the first node called head. We check if the current node exists. If yes, we print its data and move to the next node. We repeat this until we reach the end where current is None. If the list is empty, nothing prints. This process ensures all nodes are visited and their data shown in order.