Delete Node by Value in DSA C - Execution Trace

Concept Flow - Delete Node by Value

Start at head

↓

Check if head is NULL

↓

Stop

↓

Delete head

↓

Update head

↓

Stop

↓

Delete node

↓

Stop

Start from the head node, check if it matches the value to delete. If yes, delete head. Otherwise, traverse to find the node and delete it if found.

Execution Sample

DSA C

struct Node {
  int data;
  struct Node* next;
};

void deleteNode(struct Node** head, int val) {
  // delete node with value val
}

Deletes the first node with the given value from a singly linked list.

Execution Table

Step	Current Node Value	Condition	Action	List State
1	10	head != NULL	Check head value	10 -> 20 -> 30 -> 40 -> NULL
2	10	10 == 20?	No, move to next	10 -> 20 -> 30 -> 40 -> NULL
3	20	20 == 20?	Yes, delete this node	10 -> 30 -> 40 -> NULL
4	30	Continue traversal?	No, node deleted	10 -> 30 -> 40 -> NULL
5	NULL	End of list	Stop	10 -> 30 -> 40 -> NULL

💡 Node with value 20 found and deleted, traversal stops.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
head	10 -> 20 -> 30 -> 40 -> NULL	10 -> 20 -> 30 -> 40 -> NULL	10 -> 20 -> 30 -> 40 -> NULL	10 -> 30 -> 40 -> NULL	10 -> 30 -> 40 -> NULL
current	10	10	20	20	30
previous	NULL	NULL	10	10	10

Key Moments - 3 Insights

Why do we check if the head node contains the value before traversing?

Because if the head node has the value, we must update the head pointer to the next node. This is shown in execution_table steps 1-2 where the head value is checked.

What happens if the value is not found in the list?

The traversal reaches the end (NULL) without deleting any node, as shown in execution_table step 5 where the list remains unchanged and the function stops.

Why do we keep track of the previous node during traversal?

To update the previous node's next pointer to skip the deleted node. This is shown in variable_tracker where 'previous' points to the node before 'current' to adjust links.

Visual Quiz - 3 Questions

Look at the execution_table, what is the list state after deleting the node with value 20?

A 10 -> 20 -> 30 -> 40 -> NULL

B 10 -> 30 -> 40 -> NULL

C 20 -> 30 -> 40 -> NULL

D 10 -> 40 -> NULL

💡 Hint

Check the 'List State' column at step 3 in execution_table.

At which step does the traversal stop after deleting the node?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Action' column where it says 'node deleted' and traversal stops.

If the value to delete was 10 (head node), what would happen to the head pointer?

A It stays the same

B It moves to the next node

C It becomes NULL immediately

D It points to the deleted node

💡 Hint

Refer to key_moments about deleting the head node and updating the head pointer.

Concept Snapshot

Delete Node by Value in Linked List:
- Start at head node
- If head matches value, update head to next
- Else traverse list with previous and current pointers
- When node found, link previous->next to current->next
- Free deleted node
- Stop when node deleted or end reached

Full Transcript

To delete a node by value in a singly linked list, start checking from the head node. If the head node contains the value, update the head pointer to the next node and delete the head. Otherwise, traverse the list keeping track of the previous and current nodes. When the node with the target value is found, update the previous node's next pointer to skip the current node, then delete the current node. If the value is not found, the list remains unchanged. This process ensures the linked list remains connected and valid after deletion.