Insert at Middle Specific Position in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node with given data.

DSA C

struct Node* newNode(int data) {
    struct Node* node = (struct Node*)malloc(sizeof(struct Node));
    node->data = [1];
    node->next = NULL;
    return node;
}

Drag options to blanks, or click blank then click option'

Anode

BNULL

C0

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning NULL or 0 instead of the input data.

Using the variable name 'node' instead of 'data'.

The new node's data field should be set to the input parameter 'data'.

2fill in blank

medium

Complete the code to traverse the list until the position before insertion.

DSA C

struct Node* temp = head;
int i = 1;
while (i < [1] - 1 && temp != NULL) {
    temp = temp->next;
    i++;
}

Drag options to blanks, or click blank then click option'

Apos

Bdata

Chead

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'data' or 'head' instead of the position variable.

Incorrect loop condition causing infinite loop.

We traverse until the node before the desired position, so we use 'pos'.

3fill in blank

hard

Fix the error in linking the new node after the temp node.

DSA C

new_node->next = [1]->next;
[1]->next = new_node;

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Atemp

Bhead

Cnew_node

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'head' or 'new_node' instead of 'temp' causes wrong linking.

Assigning NULL breaks the list.

We link the new node after 'temp', so 'temp' is used to access the next node.

4fill in blank

hard

Fill both blanks to check if position is valid and handle insertion at head.

DSA C

if (pos == 1) {
    new_node->next = [1];
    [2] = new_node;
} else {
    // insertion in middle or end
}

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Ahead

Btemp

Cnew_node

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'temp' or 'new_node' instead of 'head' causes wrong head update.

Not updating head pointer leads to lost list.

When inserting at position 1, new_node points to current head, and head is updated to new_node.

5fill in blank

hard

Fill all three blanks to complete the insertAtPosition function.

DSA C

void insertAtPosition(struct Node** head_ref, int data, int pos) {
    struct Node* new_node = newNode(data);
    if (pos == 1) {
        new_node->next = [1];
        [2] = new_node;
        return;
    }
    struct Node* temp = *head_ref;
    int i = 1;
    while (i < pos - 1 && temp != NULL) {
        temp = temp->next;
        i++;
    }
    if (temp == NULL) {
        printf("Position out of range\n");
        free(new_node);
        return;
    }
    new_node->next = [3]->next;
    [3]->next = new_node;
}

Drag options to blanks, or click blank then click option'

A*head_ref

Ctemp

Dnew_node

Attempts:

3 left

💡 Hint

Common Mistakes

Not dereferencing head_ref correctly.

Using wrong pointer for linking new_node.

For position 1, new_node->next points to *head_ref and *head_ref is updated. For middle insertion, new_node->next and temp->next are linked.

Practice

1. What does inserting a node at a specific middle position in a linked list mean?

easy

A. Adding a new node only at the start of the list

B. Adding a new node exactly at the given position counting from the head

C. Adding a new node only at the end of the list

D. Replacing the node at the given position with a new node

Solution

1. Step 1: Understand the position concept

   Inserting at a specific position means counting nodes from the head and placing the new node exactly there.

2. Step 2: Differentiate from other insertions

   Insertion at start or end is special cases; here we insert in the middle without removing nodes.

3. Final Answer:

   Adding a new node exactly at the given position counting from the head -> Option B

4. Quick Check:

   Insert at position = Insert node at that place [OK]

Hint: Insert at position means count nodes and place new node there [OK]

Common Mistakes:

• Confusing insertion with replacement
• Thinking insertion only happens at start or end
• Ignoring the position count from head

2. Which of the following C code snippets correctly inserts a new node at position 3 in a singly linked list?

easy

A. Traverse to node 2, set newNode->next = current->next; current->next = newNode;

B. Set newNode->next = head; head = newNode;

C. Traverse to node 3, set current->next = newNode; newNode->next = NULL;

D. Set newNode->next = NULL; current->next = newNode;

Solution

1. Step 1: Identify correct traversal

   To insert at position 3, we must reach node 2 (one before position 3).

2. Step 2: Link new node correctly

   Set newNode->next to current->next, then current->next to newNode to insert properly.

3. Final Answer:

   Traverse to node 2, set newNode->next = current->next; current->next = newNode; -> Option A

4. Quick Check:

   Insert at pos 3 = link after node 2 [OK]

Hint: Insert after (position-1)th node by adjusting pointers [OK]

Common Mistakes:

• Inserting at wrong node position
• Not updating newNode->next before linking
• Setting newNode->next to NULL incorrectly

3. What will be the linked list after inserting a node with value 99 at position 3 in the list 10 -> 20 -> 30 -> 40 -> NULL?

medium

A. 99 -> 10 -> 20 -> 30 -> 40 -> NULL

B. 10 -> 20 -> 30 -> 99 -> 40 -> NULL

C. 10 -> 20 -> 30 -> 40 -> 99 -> NULL

D. 10 -> 20 -> 99 -> 30 -> 40 -> NULL

Solution

1. Step 1: Identify position 3 in the list

   Positions: 1=10, 2=20, 3=30, so new node goes before 30.

2. Step 2: Insert new node at position 3

   New node with 99 points to 30, node 20 points to new node.

3. Final Answer:

   10 -> 20 -> 99 -> 30 -> 40 -> NULL -> Option D

4. Quick Check:

   Insert at pos 3 places 99 before 30 [OK]

Hint: Insert at pos 3 means new node is third in list [OK]

Common Mistakes:

• Inserting after instead of at position
• Appending at end instead of middle
• Confusing node values and positions

4. Given the following code snippet to insert at position 2, what is the error?

void insertAtPos(Node** head, int data, int pos) {
  Node* newNode = malloc(sizeof(Node));
  newNode->data = data;
  newNode->next = NULL;
  Node* temp = *head;
  for(int i = 1; i < pos - 1; i++) {
    temp = temp->next;
  }
  newNode->next = temp->next;
  temp->next = newNode;
}

medium

A. Memory for newNode is not allocated

B. newNode->next is not set before linking

C. Loop runs one time too many causing temp to be NULL

D. Head pointer is not updated after insertion

Solution

1. Step 1: Analyze loop for position 2

   Loop should run from i=1 to i < pos-1 to stop at node before insertion point.

2. Step 2: Check temp usage after loop

   Original loop runs one time too many, moving temp to node 2 instead of node 1, causing incorrect insertion or NULL access.

3. Final Answer:

   Loop runs one time too many causing temp to be NULL -> Option C

4. Quick Check:

   Loop overshoots node before position [OK]

Hint: Loop should stop at position-1 to avoid NULL [OK]

Common Mistakes:

• Loop runs to pos instead of pos-1
• Not checking for NULL before accessing temp->next
• Forgetting to allocate memory for new node

5. You have a singly linked list with 5 nodes: 1 -> 2 -> 3 -> 4 -> 5 -> NULL. You want to insert a node with value 99 at position 6. What should happen and what will be the final list?

hard

A. Node 99 is appended at the end; list becomes 1 -> 2 -> 3 -> 4 -> 5 -> 99 -> NULL

B. Node 99 is inserted at position 5; list becomes 1 -> 2 -> 3 -> 4 -> 99 -> 5 -> NULL

C. Node 99 replaces node 5; list becomes 1 -> 2 -> 3 -> 4 -> 99 -> NULL

D. Insertion fails because position 6 is invalid; list remains unchanged

Solution

1. Step 1: Check list length and position

   List has 5 nodes; position 6 means insert after last node (append).

2. Step 2: Insert node at end

   Since position is one more than length, node 99 is added after node 5.

3. Final Answer:

   Node 99 is appended at the end; list becomes 1 -> 2 -> 3 -> 4 -> 5 -> 99 -> NULL -> Option A

4. Quick Check:

   Insert at pos > length means append [OK]

Hint: Position beyond length means append at end [OK]

Common Mistakes:

• Rejecting valid append position
• Replacing last node instead of appending
• Inserting at wrong position due to off-by-one