Delete by Value in Doubly Linked List in DSA Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a doubly linked list?

A doubly linked list is a chain of nodes where each node has three parts: data, a pointer to the next node, and a pointer to the previous node. This allows moving forward and backward through the list.

beginner

What does 'delete by value' mean in a doubly linked list?

It means finding the first node that contains a specific value and removing that node from the list, adjusting the links so the list stays connected.

intermediate

Which pointers need to be updated when deleting a node in a doubly linked list?

You must update the previous node's next pointer to skip the deleted node and point to the deleted node's next node. Also, update the next node's previous pointer to point to the deleted node's previous node.

intermediate

What should you do if the node to delete is the head of the doubly linked list?

Update the head pointer to the next node and set the new head's previous pointer to null if the new head is not null.

beginner

What happens if the value to delete is not found in the doubly linked list?

No nodes are deleted, and the list remains unchanged.

In a doubly linked list, what pointers does each node have?

A No pointers

B Only next pointer

C Only previous pointer

D Next and previous pointers

Each node in a doubly linked list has two pointers: one to the next node and one to the previous node.

When deleting a node by value, what is the first step?

A Update all pointers immediately

B Find the node with the given value

C Delete the head node

D Create a new node

You must first find the node that contains the value before deleting it.

If the node to delete is the last node, what should you update?

A Set the previous node's next pointer to null

B Set the next node's previous pointer to null

C Set the head pointer to null

D No updates needed

The previous node's next pointer should be set to null to mark the end of the list.

What happens if you delete the only node in a doubly linked list?

A The list becomes empty (head is null)

B The list still has one node

C The list becomes circular

D The list is unchanged

Deleting the only node leaves the list empty, so the head pointer becomes null.

Which pointer must be updated if the node to delete is in the middle of the list?

A No pointers need updating

B Only the head pointer

C Both previous node's next and next node's previous pointers

D Only the tail pointer

Both the previous node's next and the next node's previous pointers must be updated to bypass the deleted node.

Explain step-by-step how to delete a node by value in a doubly linked list.

Think about how the links before and after the node change.

What special cases must you consider when deleting a node by value in a doubly linked list?

Consider positions of the node in the list.

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