Delete by Value in Doubly Linked List in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the list is empty before deletion.

DSA Java

if (head == [1]) {
    System.out.println("List is empty");
    return;
}

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

Avalue

Bhead

Cnull

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if head equals tail instead of null.

Using value variable instead of head.

We check if head is null to know if the list is empty.

2fill in blank

medium

Complete the code to traverse the list to find the node with the given value.

DSA Java

Node current = head;
while (current != [1] && current.data != value) {
    current = current.next;
}

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

Anull

Bhead

Ctail

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using head instead of null in the loop condition.

Comparing current.data with head instead of value.

We traverse until current is null or we find the value.

3fill in blank

hard

Fix the error in updating the previous node's next pointer when deleting a middle node.

DSA Java

if (current.prev != null) {
    current.prev.[1] = current.next;
}

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

Anext

Bprev

Cdata

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Updating prev pointer instead of next.

Trying to update data or value fields.

We update the previous node's next pointer to skip the current node.

4fill in blank

hard

Fill both blanks to update the next node's previous pointer and handle tail update.

DSA Java

if (current.next != null) {
    current.next.[1] = current.prev;
} else {
    tail = [2];
}

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

Aprev

Bnext

Ccurrent.prev

Dcurrent.next

Attempts:

3 left

💡 Hint

Common Mistakes

Using next instead of prev for next node's pointer.

Setting tail to current.next instead of current.prev.

We update the next node's prev pointer to current's prev and update tail if current is last.

5fill in blank

hard

Fill all three blanks to handle deleting the head node and freeing the current node.

DSA Java

if (current == head) {
    head = [1];
}
current.[2] = null;
current.[3] = null;

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

Acurrent.next

Bprev

Cnext

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Not updating head when deleting first node.

Clearing data instead of pointers.

Mixing prev and next pointers.

When deleting head, update head to next node. Then clear current's prev and next to help garbage collection.

Practice

1. What happens when you delete a node by value in a doubly linked list?

easy

A. The node with the matching value is removed and links are updated

B. All nodes are deleted regardless of value

C. Only the first node is deleted no matter the value

D. The list is reversed instead of deleting

Solution

1. Step 1: Locate the node with the given value

   Traverse the list from head to tail to find the node whose data matches the value to delete.

2. Step 2: Update links to remove the node

   Adjust the previous node's next pointer and the next node's previous pointer to bypass the node to be deleted.

3. Final Answer:

   The node with the matching value is removed and links are updated -> Option A

4. Quick Check:

   Deleting by value removes matching node [OK]

Hint: Find node by value, then update previous and next links [OK]

Common Mistakes:

• Not updating both previous and next pointers
• Deleting all nodes instead of one
• Ignoring the case when node is head or tail

2. Which of the following is the correct Java syntax to delete a node by value in a doubly linked list?

easy

A. int deleteByValue(int value) { /* code */ }

B. void deleteByValue(int value) { /* code */ }

C. deleteByValue(int value) { /* code */ }

D. void deleteByValue() { /* code */ }

Solution

1. Step 1: Check method return type and parameters

   The method should accept an integer value to delete and return nothing, so void return type is correct.

2. Step 2: Verify method signature syntax

   Java requires return type before method name and parameter types inside parentheses.

3. Final Answer:

   void deleteByValue(int value) { /* code */ } -> Option B

4. Quick Check:

   Method with void return and int parameter is correct [OK]

Hint: Method must specify return type and parameter types in Java [OK]

Common Mistakes:

• Omitting return type
• Missing parameter type
• Using wrong return type for delete method

3. Given the doubly linked list: 10 <-> 20 <-> 30 <-> 40 <-> null, what is the list after deleting the node with value 30?

medium

A. 10 <-> 20 <-> 40 <-> null

B. 10 <-> 20 <-> 30 <-> 40 <-> null

C. 20 <-> 30 <-> 40 <-> null

D. 10 <-> 40 <-> null

Solution

1. Step 1: Identify node with value 30

   Traverse the list and find the node containing 30 between 20 and 40.

2. Step 2: Remove node 30 and update links

   Set 20's next pointer to 40 and 40's previous pointer to 20, removing 30 from the chain.

3. Final Answer:

   10 <-> 20 <-> 40 <-> null -> Option A

4. Quick Check:

   Node 30 removed, links updated correctly [OK]

Hint: Remove node and link previous to next nodes directly [OK]

Common Mistakes:

• Not updating previous pointer of next node
• Leaving deleted node linked
• Deleting wrong node

4. What is the error in this code snippet for deleting a node by value in a doubly linked list?

void deleteByValue(int value) {
  Node current = head;
  while (current != null && current.data != value) {
    current = current.next;
  }
  if (current == null) return;
  current.prev.next = current.next;
  current.next.prev = current.prev;
}

medium

A. It reverses the list instead of deleting

B. It does not check if current is null before accessing pointers

C. It deletes all nodes with the value instead of one

D. It does not handle deletion when current is head

Solution

1. Step 1: Analyze deletion at head node

   If current is head, current.prev is null, so current.prev.next causes NullPointerException.

2. Step 2: Identify missing condition for head deletion

   Code must check if current.prev is null and update head pointer accordingly.

3. Final Answer:

   It does not handle deletion when current is head -> Option D

4. Quick Check:

   Head deletion needs special handling [OK]

Hint: Check if node is head before updating previous pointer [OK]

Common Mistakes:

• Not handling head or tail nodes separately
• Accessing null pointers without checks
• Assuming node always has previous and next

5. You have a doubly linked list: 5 <-> 10 <-> 15 <-> 20 <-> 25 <-> null. You want to delete the node with value 5, then delete the node with value 25. What is the final list?

hard

A. null

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

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

D. 10 <-> 15 <-> 20 <-> 25 <-> null

Solution

1. Step 1: Delete node with value 5 (head)

   Since 5 is head, update head to 10 and set 10's prev to null.

2. Step 2: Delete node with value 25 (tail)

   Since 25 is tail, update 20's next to null, removing 25.

3. Final Answer:

   10 <-> 15 <-> 20 <-> null -> Option C

4. Quick Check:

   Head and tail deletions handled correctly [OK]

Hint: Update head or tail pointers when deleting first or last node [OK]

Common Mistakes:

• Not updating head when deleting first node
• Not updating tail when deleting last node
• Breaking links causing list corruption