Delete Node at Specific Position in DSA C - Execution Trace

Concept Flow - Delete Node at Specific Position

Start

↓

Check if list empty

No↓

Check if position is 1

↓

Delete head

↓

Update head

↓

Free node

↓

End

↓

End

The flow checks if the list is empty or if the position is the first node, deletes accordingly, otherwise traverses to the node before the target and deletes the target node.

Execution Sample

DSA C

void deleteAtPosition(Node** head, int pos) {
  if (*head == NULL) return;
  Node* temp = *head;
  if (pos == 1) {
    *head = temp->next;
    free(temp);
    return;
  }
  for (int i = 1; temp != NULL && i < pos - 1; i++)
    temp = temp->next;
  if (temp == NULL || temp->next == NULL) return;
  Node* next = temp->next->next;
  free(temp->next);
  temp->next = next;
}

Deletes the node at the given position in a singly linked list.

Execution Table

Step	pos	temp points to	Condition Checked	Action	List State
1	3	Node 1 (value=10)	*head != NULL	Continue	10 -> 20 -> 30 -> 40 -> null
2	3	Node 1 (value=10)	pos == 1	No	10 -> 20 -> 30 -> 40 -> null
3	3	Node 1 (value=10)	i=1 < pos-1=2	temp = temp->next (Node 2)	10 -> 20 -> 30 -> 40 -> null
4	3	Node 2 (value=20)	i=2 < pos-1=2	Loop ends	10 -> 20 -> 30 -> 40 -> null
5	3	Node 2 (value=20)	temp != NULL && temp->next != NULL	Yes	10 -> 20 -> 30 -> 40 -> null
6	3	Node 2 (value=20)	Prepare to delete Node 3 (value=30)	next = Node 4	10 -> 20 -> 30 -> 40 -> null
7	3	Node 2 (value=20)	free(Node 3)	Delete Node 3	10 -> 20 -> 40 -> null
8	3	Node 2 (value=20)	temp->next = next	Link Node 2 to Node 4	10 -> 20 -> 40 -> null
9	3	-	End of function	Return	10 -> 20 -> 40 -> null

💡 Function ends after deleting node at position 3 and updating links.

Variable Tracker

Variable	Start	After Step 3	After Step 4	After Step 6	Final
pos	3	3	3	3	3
temp	Node 1 (10)	Node 2 (20)	Node 2 (20)	Node 2 (20)	Node 2 (20)
next	NULL	NULL	NULL	Node 4 (40)	Node 4 (40)
*head	Node 1 (10)	Node 1 (10)	Node 1 (10)	Node 1 (10)	Node 1 (10)

Key Moments - 3 Insights

Why do we check if temp == NULL or temp->next == NULL before deleting?

Because if temp is NULL or temp->next is NULL, it means the position is beyond the list length, so no deletion happens. See execution_table row 5 where this check prevents errors.

Why do we handle position 1 separately?

Position 1 means deleting the head node, so we update the head pointer directly. This is shown in execution_table row 2 where pos == 1 is checked.

How does the loop find the node before the one to delete?

The loop runs pos-2 times moving temp forward, so temp points to the node before the target. See execution_table rows 3 and 4 for temp moving from Node 1 to Node 2.

Visual Quiz - 3 Questions

Look at the execution_table, what node does temp point to after the loop ends?

A Node 3 (value=30)

B Node 1 (value=10)

C Node 2 (value=20)

D Node 4 (value=40)

💡 Hint

Check execution_table rows 3 and 4 where temp moves and loop ends.

At which step is the node at position 3 deleted?

A Step 5

B Step 7

C Step 6

D Step 8

💡 Hint

Look at execution_table row 7 where free(Node 3) happens.

If pos was 1, what would happen to the head pointer?

A It would point to the second node

B It would point to NULL

C It would remain unchanged

D It would point to the last node

💡 Hint

Refer to key_moments about position 1 deletion and execution_table row 2.

Concept Snapshot

Delete Node at Specific Position in Linked List:
- If list empty, do nothing
- If pos == 1, update head to next node and free old head
- Else, move to (pos-1)th node
- If next node exists, unlink and free node at pos
- Update links to maintain list integrity

Full Transcript

This concept shows how to delete a node at a specific position in a singly linked list. First, it checks if the list is empty. If the position is 1, it deletes the head node by updating the head pointer. Otherwise, it moves to the node before the target position. If the target node exists, it unlinks it from the list and frees its memory. The execution table traces each step, showing how the pointer moves and how the list changes after deletion. Key moments clarify why certain checks are needed to avoid errors. The visual quiz tests understanding of pointer positions and list updates during deletion.