Insert at End of 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->next = NULL;
newNode->prev = NULL;

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

Adata

BNULL

Chead

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning NULL or other pointers instead of the data value.

Forgetting to assign the data field.

The new node's data field should be set to the given data value.

2fill in blank

medium

Complete the code to check if the list is empty.

DSA C

if (*head == [1]) {
    *head = newNode;
    return;
}

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

Atemp

BNULL

Chead

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing head to newNode or other pointers.

Using assignment '=' instead of comparison '=='.

If *head is NULL, the list is empty and the new node becomes the head.

3fill in blank

hard

Fix the error in the loop that finds the last node.

DSA C

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

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

Aprev

Bdata

Cnext

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using temp->prev which moves backward.

Checking temp->data instead of pointers.

To find the last node, traverse while temp->next is not NULL.

4fill in blank

hard

Fill both blanks to link the new node at the end.

DSA C

temp->next = [1];
[2]->prev = temp;

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

AnewNode

Bhead

Ctemp

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Linking to head or temp incorrectly.

Not updating both next and prev pointers.

The last node's next points to newNode, and newNode's prev points back to last node.

5fill in blank

hard

Fill all three blanks to complete the insert at end function.

DSA C

void insertEnd(struct Node** head, int data) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = [1];
    newNode->next = NULL;
    newNode->prev = NULL;

    if (*head == [2]) {
        *head = newNode;
        return;
    }

    struct Node* temp = *head;
    while (temp->next != NULL) {
        temp = temp->next;
    }

    temp->next = [3];
    newNode->prev = temp;
}

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

Adata

BNULL

CnewNode

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to dereference head pointer.

Linking temp->next to wrong node.

Not setting newNode->prev correctly.

Assign data to newNode->data, check if *head is NULL, and link temp->next to newNode.

Practice

1. What is the main purpose of inserting a node at the end of a doubly linked list?

easy

A. To add a new element after the last node

B. To remove the first node

C. To reverse the list

D. To find the middle node

Solution

1. Step 1: Understand the list structure

   A doubly linked list has nodes connected forward and backward, allowing traversal in both directions.

2. Step 2: Purpose of insertion at end

   Inserting at the end means adding a new node after the last node, extending the list.

3. Final Answer:

   To add a new element after the last node -> Option A

4. Quick Check:

   Insert at end = add after last node [OK]

Hint: Insert at end means add after last node [OK]

Common Mistakes:

• Confusing insertion at end with deletion
• Thinking insertion happens at the start
• Mixing up singly and doubly linked list operations

2. Which of the following is the correct way to update the 'next' pointer of the last node when inserting a new node at the end in C?

easy

A. last->next = newNode;

B. newNode->next = last;

C. last->prev = newNode;

D. newNode->prev = NULL;

Solution

1. Step 1: Identify the last node's next pointer

   The last node's 'next' pointer should point to the new node to link it at the end.

2. Step 2: Correct pointer assignment

   Assigning 'last->next = newNode;' correctly links the new node after the last node.

3. Final Answer:

   last->next = newNode; -> Option A

4. Quick Check:

   Last node's next points to new node [OK]

Hint: Last node's next points to new node [OK]

Common Mistakes:

• Assigning newNode->next to last (wrong direction)
• Changing last->prev instead of last->next
• Setting newNode->prev to NULL instead of last

3. What will be the output of the following code snippet after inserting a node with value 5 at the end of the doubly linked list 1 <-> 3 <-> 4?

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

void insertEnd(struct Node** head, int val) {
  struct Node* newNode = malloc(sizeof(struct Node));
  newNode->data = val;
  newNode->next = NULL;
  if (*head == NULL) {
    newNode->prev = NULL;
    *head = newNode;
    return;
  }
  struct Node* temp = *head;
  while (temp->next != NULL) {
    temp = temp->next;
  }
  temp->next = newNode;
  newNode->prev = temp;
}

void printList(struct Node* head) {
  while (head != NULL) {
    printf("%d ", head->data);
    head = head->next;
  }
}

int main() {
  struct Node* head = malloc(sizeof(struct Node));
  head->data = 1; head->prev = NULL;
  struct Node* second = malloc(sizeof(struct Node));
  second->data = 3; second->prev = head; head->next = second;
  struct Node* third = malloc(sizeof(struct Node));
  third->data = 4; third->prev = second; second->next = third; third->next = NULL;
  insertEnd(&head, 5);
  printList(head);
  return 0;
}

medium

A. 1 3 4 0

B. 1 3 4 5

C. 1 3 4

D. 5 1 3 4

Solution

1. Step 1: Understand initial list and insertion

   The list is 1 <-> 3 <-> 4. The function inserts 5 at the end by traversing to last node (4) and linking new node after it.

2. Step 2: Trace printList output

   After insertion, list is 1 <-> 3 <-> 4 <-> 5. Printing nodes in order outputs "1 3 4 5 "

3. Final Answer:

   1 3 4 5 -> Option B

4. Quick Check:

   List after insertEnd = 1 3 4 5 [OK]

Hint: Traverse to last, link new node, print all nodes [OK]

Common Mistakes:

• Not setting newNode->prev correctly
• Forgetting to set last node's next to newNode
• Printing before insertion

4. Identify the error in the following code snippet for inserting a node at the end of a doubly linked list:

void insertEnd(struct Node** head, int val) {
  struct Node* newNode = malloc(sizeof(struct Node));
  newNode->data = val;
  newNode->next = NULL;
  if (*head == NULL) {
    *head = newNode;
    return;
  }
  struct Node* temp = *head;
  while (temp->next != NULL) {
    temp = temp->next;
  }
  temp->next = newNode;
}

medium

A. Wrong condition in while loop

B. Incorrect malloc size

C. Missing setting newNode->prev pointer

D. Not updating head pointer

Solution

1. Step 1: Check pointer assignments for doubly linked list

   In doubly linked list, newNode->prev must point to the last node (temp) after insertion.

2. Step 2: Identify missing pointer update

   The code sets temp->next = newNode but does not set newNode->prev = temp, breaking backward link.

3. Final Answer:

   Missing setting newNode->prev pointer -> Option C

4. Quick Check:

   newNode->prev must be set [OK]

Hint: Always set newNode->prev to last node [OK]

Common Mistakes:

• Forgetting newNode->prev assignment
• Assuming singly linked list logic applies
• Not handling empty list case

5. Given a doubly linked list with nodes 10 <-> 20 <-> 30, write the sequence of pointer changes when inserting a new node with value 40 at the end. Which of the following correctly describes the final connections?

hard

A. newNode->prev = NULL; newNode->next = NULL; last->next = NULL

B. newNode->next = last; last->prev = newNode; newNode->prev = NULL

C. last->prev = newNode; newNode->next = last; newNode->prev = NULL

D. last->next = newNode; newNode->prev = last; newNode->next = NULL

Solution

1. Step 1: Identify last node and new node pointers

   Last node is 30. New node 40 should be linked after 30 with next NULL.

2. Step 2: Correct pointer assignments

   Set last->next = newNode to link forward, newNode->prev = last for backward link, and newNode->next = NULL as it is new end.

3. Final Answer:

   last->next = newNode; newNode->prev = last; newNode->next = NULL -> Option D

4. Quick Check:

   New node linked after last with proper prev and next [OK]

Hint: New node's prev = last; last's next = new node; new node's next = NULL [OK]

Common Mistakes:

• Reversing prev and next pointers
• Setting newNode->prev to NULL incorrectly
• Not setting last->next to newNode