Why Delete Node at Specific Position in DSA C?

The Big Idea

What if you could remove any item from a list perfectly every time, without counting or mistakes?

The Scenario

Imagine you have a paper list of your favorite songs. You want to remove the 3rd song, but you have to count each song and erase it manually. If the list is long, this takes a lot of time and you might erase the wrong song by mistake.

The Problem

Manually counting and deleting items is slow and easy to mess up. You might lose track of the position or accidentally remove the wrong item. Also, fixing the list after deletion is tricky without a clear method.

The Solution

Using a linked list and a function to delete a node at a specific position makes this task simple and safe. The function automatically finds the right node and removes it, keeping the list connected without errors.

Before vs After

✗ Before

int i = 1;
Node* temp = head;
while (i < pos - 1 && temp != NULL) {
  temp = temp->next;
  i++;
}
// manually adjust pointers and free node

✓ After

void deleteNodeAtPosition(Node** head, int pos) {
  // function finds and deletes node at pos safely
}

What It Enables

This lets you quickly and safely remove any item from a list without losing track or breaking the list.

Real Life Example

Think of a playlist app where you want to delete the 5th song. The app uses this method to remove the song instantly without messing up the order.

Key Takeaways

Manual deletion is slow and error-prone.

Deleting at a position with a function is safe and fast.

It keeps the list connected and easy to manage.

Practice

1. What happens when you delete a node at position 1 in a singly linked list?

easy

A. The list remains unchanged

B. The last node is removed

C. The head node is removed and the next node becomes the new head

D. All nodes are deleted

Solution

1. Step 1: Understand position 1 in linked list

   Position 1 refers to the head node of the list.

2. Step 2: Deleting the head node

   Removing the head means the next node becomes the new head.

3. Final Answer:

   The head node is removed and the next node becomes the new head -> Option C

4. Quick Check:

   Deleting position 1 removes head [OK]

Hint: Deleting position 1 always removes the head node [OK]

Common Mistakes:

• Thinking position 1 deletes the last node
• Assuming list stays same after deletion
• Deleting all nodes instead of one

2. Which of the following is the correct syntax to delete a node at position pos in a singly linked list in C?

easy

A. void deleteNode(struct Node* head, int pos);

B. void deleteNode(struct Node** head_ref, int pos);

C. void deleteNode(int pos, struct Node* head);

D. void deleteNode(int pos);

Solution

1. Step 1: Understand pointer usage for head modification

   To delete a node, the function must modify the head pointer if position 1 is deleted, so it needs a pointer to pointer.

2. Step 2: Check function parameters

   Only void deleteNode(struct Node** head_ref, int pos); uses struct Node** head_ref allowing head modification.

3. Final Answer:

   void deleteNode(struct Node** head_ref, int pos); -> Option B

4. Quick Check:

   Use pointer to pointer for head changes [OK]

Hint: Use double pointer to head to delete at any position [OK]

Common Mistakes:

• Using single pointer and expecting head to change
• Wrong parameter order
• Missing head pointer in parameters

3. Given the linked list: 10 -> 20 -> 30 -> 40 -> 50 -> NULL, what is the list after deleting the node at position 3?

medium

A. 10 -> 20 -> 40 -> 50 -> NULL

B. 10 -> 20 -> 30 -> 50 -> NULL

C. 10 -> 30 -> 40 -> 50 -> NULL

D. 20 -> 30 -> 40 -> 50 -> NULL

Solution

1. Step 1: Identify node at position 3

   Position 3 node is 30 in the list.

2. Step 2: Remove node 30 and link previous to next

   Link node 20 to node 40, skipping 30.

3. Final Answer:

   10 -> 20 -> 40 -> 50 -> NULL -> Option A

4. Quick Check:

   Deleted 3rd node (30) correctly [OK]

Hint: Skip the node at position by linking previous to next [OK]

Common Mistakes:

• Deleting wrong node position
• Not updating links correctly
• Removing head instead of position 3

4. Consider this code snippet to delete a node at position pos in a linked list:

void deleteNode(struct Node** head_ref, int pos) {
  struct Node* temp = *head_ref;
  if (pos == 1) {
    *head_ref = 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;
  struct Node* next = temp->next->next;
  free(temp->next);
  temp->next = next;
}

What is the bug in this code?

medium

A. It does not handle empty list when pos is 1

B. It frees the wrong node

C. It does not update head pointer correctly

D. It does not check if pos is valid

Solution

1. Step 1: Check deletion at position 1

   If list is empty (*head_ref is NULL), temp is NULL, so temp->next causes error.

2. Step 2: Identify missing empty list check

   Code should check if temp is NULL before accessing temp->next when pos == 1.

3. Final Answer:

   It does not handle empty list when pos is 1 -> Option A

4. Quick Check:

   Empty list check missing at head deletion [OK]

Hint: Always check if list is empty before deleting [OK]

Common Mistakes:

• Ignoring empty list case
• Assuming pos is always valid
• Not freeing the deleted node

5. You have a singly linked list: 5 -> 10 -> 15 -> 20 -> 25 -> NULL. You want to delete the node at position 6. What should happen after calling the delete function?

hard

A. The last node (25) is deleted

B. The function crashes due to invalid position

C. The head node (5) is deleted

D. The list remains unchanged because position 6 is invalid

Solution

1. Step 1: Check if position 6 exists in list

   List has 5 nodes, so position 6 is invalid.

2. Step 2: Behavior on invalid position

   Proper delete function should do nothing if position is invalid, leaving list unchanged.

3. Final Answer:

   The list remains unchanged because position 6 is invalid -> Option D

4. Quick Check:

   Invalid position means no deletion [OK]

Hint: Invalid position means no change to list [OK]

Common Mistakes:

• Deleting last node incorrectly
• Crashing due to no position check
• Deleting head by mistake