Insert at Specific Position in Doubly Linked List 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 = (struct Node*)malloc(sizeof(struct Node));
newNode->data = [1];
newNode->prev = NULL;
newNode->next = NULL;

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

Atemp

Bnode

Cpos

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using a pointer variable instead of the data value.

Assigning position or temporary node instead of data.

The new node's data field should be assigned the value passed as 'data'.

2fill in blank

medium

Complete the code to insert the new node at the beginning of the list.

DSA C

if (pos == 1) {
    newNode->next = [1];
    if (head != NULL) {
        head->prev = newNode;
    }
    head = newNode;
    return head;
}

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

Ahead

Btemp

CnewNode

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Setting newNode->next to itself.

Setting newNode->next to NULL incorrectly.

The new node's next pointer should point to the current head node.

3fill in blank

hard

Fix the error in updating the previous pointer of the node after the new node.

DSA C

newNode->next = temp->next;
if (temp->next != NULL) {
    temp->next->[1] = newNode;
}
temp->next = newNode;
newNode->prev = temp;

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

Aprev

Bnext

Cdata

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Updating the next pointer instead of prev.

Not checking if temp->next is NULL before updating.

The previous pointer of the node after newNode should point back to newNode.

4fill in blank

hard

Fill both blanks to traverse to the node before the insertion position.

DSA C

struct Node* temp = head;
for (int i = 1; i < [1] - 1; i++) {
    temp = [2];
}

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

Apos

Btemp->next

Chead

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong loop limit or variable.

Moving temp incorrectly.

We loop until the node before position 'pos', moving temp to temp->next each time.

5fill in blank

hard

Fill all three blanks to insert the new node at the given position in the doubly linked list.

DSA C

newNode->next = [1];
if ([2] != NULL) {
    [3]->prev = newNode;
}
temp->next = newNode;
newNode->prev = temp;

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

Atemp->next

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using head instead of temp->next.

Not updating prev pointer of the next node.

The new node's next points to temp->next; if temp->next is not NULL, its prev points to newNode.

Practice

1. What happens when you insert a new node at position 1 in a doubly linked list?

easy

A. The new node becomes the new head of the list.

B. The new node is added at the end of the list.

C. The new node replaces the last node.

D. The list remains unchanged.

Solution

1. Step 1: Understand position 1 insertion

   Inserting at position 1 means adding the node at the start of the list.

2. Step 2: Effect on head pointer

   The new node becomes the head, and its next points to the old head.

3. Final Answer:

   The new node becomes the new head of the list. -> Option A

4. Quick Check:

   Position 1 insertion updates head [OK]

Hint: Position 1 means new head insertion [OK]

Common Mistakes:

• Thinking position 1 means end insertion
• Not updating the head pointer
• Ignoring previous pointer updates

2. Which of the following is the correct way to update pointers when inserting a node at position 3 in a doubly linked list?

easy

A. newNode->next = temp; newNode->prev = temp->prev; temp->prev->next = newNode; temp->prev = newNode;

B. newNode->prev = temp->prev; newNode->next = temp; temp->prev->next = newNode; temp->prev = newNode;

C. newNode->next = temp->next; newNode->prev = temp; temp->next->prev = newNode; temp->next = newNode;

D. newNode->next = temp->next; newNode->prev = temp->prev; temp->next = newNode; temp->prev = newNode;

Solution

1. Step 1: Identify insertion point

   At position 3, newNode is inserted after temp (node at position 2).

2. Step 2: Update pointers correctly

   newNode's next points to temp's next, prev to temp; temp's next's prev updated to newNode; temp's next updated to newNode.

3. Final Answer:

   newNode->next = temp->next; newNode->prev = temp; temp->next->prev = newNode; temp->next = newNode; -> Option C

4. Quick Check:

   Correct pointer updates for middle insertion [OK]

Hint: Update newNode next/prev before changing temp pointers [OK]

Common Mistakes:

• Swapping next and prev pointers
• Not updating temp->next->prev
• Forgetting to update temp->next

3. What will be the list after inserting a node with value 10 at position 2 in the doubly linked list: 5 <-> 15 <-> 20?

medium

A. 5 <-> 15 <-> 10 <-> 20

B. 10 <-> 5 <-> 15 <-> 20

C. 5 <-> 15 <-> 20 <-> 10

D. 5 <-> 10 <-> 15 <-> 20

Solution

1. Step 1: Locate position 2

   Position 2 means new node goes between nodes 1 (5) and 2 (15).

2. Step 2: Insert new node with value 10

   New node's prev points to 5, next points to 15; update 5's next and 15's prev accordingly.

3. Final Answer:

   5 <-> 10 <-> 15 <-> 20 -> Option D

4. Quick Check:

   Inserted node at position 2 between 5 and 15 [OK]

Hint: Position 2 means between first and second nodes [OK]

Common Mistakes:

• Inserting at wrong position
• Not updating both next and prev pointers
• Appending instead of inserting

4. Given the code snippet below, what is the error when inserting at position 4 in a list of 3 nodes?

void insertAtPosition(Node** head, int data, int pos) {
  Node* newNode = createNode(data);
  Node* temp = *head;
  for (int i = 1; i < pos - 1; i++) {
    temp = temp->next;
  }
  newNode->next = temp->next;
  newNode->prev = temp;
  temp->next->prev = newNode;
  temp->next = newNode;
}

medium

A. newNode is not allocated properly.

B. temp->next is NULL, so temp->next->prev causes a runtime error.

C. Loop runs one time too many causing segmentation fault.

D. prev pointer of newNode is not set.

Solution

1. Step 1: Analyze loop for position 4 in 3-node list

   Loop moves temp to node at position 3; temp->next is NULL (end of list).

2. Step 2: Check pointer updates

   Accessing temp->next->prev causes runtime error because temp->next is NULL.

3. Final Answer:

   temp->next is NULL, so temp->next->prev causes a runtime error. -> Option B

4. Quick Check:

   Accessing NULL pointer causes runtime error [OK]

Hint: Check for NULL before accessing next->prev [OK]

Common Mistakes:

• Not checking if temp->next is NULL
• Assuming list is longer than it is
• Ignoring edge case at list end

5. You have a doubly linked list: 1 <-> 3 <-> 5 <-> 7. You want to insert a node with value 4 at position 3. After insertion, what will be the correct list and how do you handle the pointers to maintain list integrity?

hard

A. 1 <-> 3 <-> 4 <-> 5 <-> 7; Set newNode->prev = node at pos 2, newNode->next = node at pos 3, update adjacent nodes' pointers.

B. 1 <-> 3 <-> 5 <-> 4 <-> 7; Insert newNode after node at pos 3 without updating prev pointers.

C. 1 <-> 4 <-> 3 <-> 5 <-> 7; Insert newNode at head and shift others.

D. 1 <-> 3 <-> 5 <-> 7 <-> 4; Append newNode at end regardless of position.

Solution

1. Step 1: Identify insertion position and nodes

   Position 3 means new node goes between nodes with values 3 (pos 2) and 5 (pos 3).

2. Step 2: Update pointers to insert new node

   Set newNode->prev to node with value 3, newNode->next to node with value 5; update node 3's next and node 5's prev to newNode.

3. Step 3: Verify list integrity

   After insertion, list is 1 <-> 3 <-> 4 <-> 5 <-> 7 with all pointers correctly linked.

4. Final Answer:

   1 <-> 3 <-> 4 <-> 5 <-> 7; Set newNode->prev = node at pos 2, newNode->next = node at pos 3, update adjacent nodes' pointers. -> Option A

5. Quick Check:

   Proper pointer updates maintain doubly linked list [OK]

Hint: Insert between nodes, update both next and prev pointers [OK]

Common Mistakes:

• Inserting at wrong position
• Not updating both adjacent nodes' pointers
• Breaking list links causing traversal errors