Delete by Value in Doubly Linked List in DSA Rust - 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 a value and two links: one to the next node and one 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 it from the list, adjusting the links of neighboring nodes to keep the list connected.

intermediate

In Rust, why do we use Option and Box for nodes in a doubly linked list?

Option is used because a node's next or previous link can be empty (None). Box is used to own the node data on the heap, allowing nodes to be linked dynamically.

intermediate

What steps are needed to delete a node by value in a doubly linked list?

1. Find the node with the target value. 2. If found, update the previous node's next link to skip the node. 3. Update the next node's previous link to skip the node. 4. Remove the node safely.

intermediate

What happens if the node to delete is the head or tail of the doubly linked list?

If it's the head, update the head pointer to the next node. If it's the tail, update the tail pointer to the previous node. Adjust links accordingly to keep the list valid.

What links does a node in a doubly linked list have?

A Only previous node

B Only next node

C Next and previous nodes

D No links

Each node has two links: one to the next node and one to the previous node.

What Rust type is used to represent a link that might be empty in a doubly linked list?

A Box

B Vec

C Result

D Option

Option is used to represent links that can be None (empty) or Some(node).

When deleting a node by value, what must you update in the neighboring nodes?

A Only the previous node's next link

B Both previous node's next link and next node's previous link

C Only the next node's previous link

D No links need updating

Both links must be updated to bypass the deleted node and keep the list connected.

If the node to delete is the head, what should you do?

A Update the head to the next node

B Do nothing

C Update the tail to the previous node

D Delete the entire list

The head pointer must move to the next node after deleting the current head.

What is the time complexity of deleting a node by value in a doubly linked list?

A O(n)

B O(n^2)

C O(log n)

D O(1)

You may need to search through the list to find the node, which takes O(n) time.

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

Think about how links before and after the node change.

Describe why a doubly linked list is useful compared to a singly linked list when deleting nodes.

Consider how having two links helps in deletion.

Practice

1. What is the main purpose of the delete_by_value function in a doubly linked list?

easy

A. To remove the first node that contains the given value

B. To add a new node with the given value at the end

C. To reverse the entire doubly linked list

D. To count how many nodes have the given value

Solution

1. Step 1: Understand the function's goal

   The delete_by_value function searches for a node with the specified value.

2. Step 2: Identify the action performed

   Once found, it removes that node from the doubly linked list, adjusting pointers accordingly.

3. Final Answer:

   To remove the first node that contains the given value -> Option A

4. Quick Check:

   Delete by value means remove matching node [OK]

Hint: Delete by value removes first matching node [OK]

Common Mistakes:

• Confusing delete with insert
• Thinking it reverses the list
• Assuming it counts nodes

2. Which Rust syntax correctly declares a mutable doubly linked list node struct with prev and next pointers?

easy

A. struct Node { value: i32, prev: Option>, next: Option> }

B. struct Node { value: i32, prev: Option<*mut Node>, next: Option<*mut Node> }

C. struct Node { value: i32, prev: Option, next: Option }

D. struct Node { value: i32, prev: Option<Node>, next: Option<Node> }

Solution

1. Step 1: Understand Rust pointer types for doubly linked lists

   Rust needs shared ownership and mutability for prev and next pointers, so Rc is used.

2. Step 2: Check options for correct pointer usage

   struct Node { value: i32, prev: Option>, next: Option> } uses Option> which allows multiple owners and interior mutability, suitable for doubly linked lists.

3. Final Answer:

   struct Node { value: i32, prev: Option>, next: Option> } -> Option A

4. Quick Check:

   Use Rc and RefCell for mutable shared nodes [OK]

Hint: Use Rc for mutable shared pointers [OK]

Common Mistakes:

• Using Box for both prev and next causes ownership issues
• Using raw pointers without unsafe code
• Using direct Node type causing infinite size

3. Given the following Rust code snippet for deleting a value from a doubly linked list, what will be the printed list after deleting value 3?

let mut list = DoublyLinkedList::new();
list.push_back(1);
list.push_back(3);
list.push_back(5);
list.delete_by_value(3);
list.print();

medium

A. 1 -> 3 -> 5 -> null

B. 1 -> 5 -> null

C. 3 -> 5 -> null

D. 1 -> null

Solution

1. Step 1: Understand initial list state

   After pushing 1, 3, 5, the list is 1 -> 3 -> 5 -> null.

2. Step 2: Delete node with value 3

   The delete_by_value(3) removes the node containing 3, linking 1 directly to 5.

3. Final Answer:

   1 -> 5 -> null -> Option B

4. Quick Check:

   Deleted 3, list is 1 -> 5 [OK]

Hint: Deleting value removes that node, links neighbors [OK]

Common Mistakes:

• Not updating prev and next pointers correctly
• Deleting wrong node or none
• Printing old list without deletion

4. Consider this Rust function snippet for deleting a node by value in a doubly linked list:

fn delete_by_value(&mut self, val: i32) {
    let mut current = self.head.clone();
    while let Some(node) = current {
        if node.borrow().value == val {
            // deletion logic here
            break;
        }
        current = node.borrow().next.clone();
    }
}

What is a common bug if the deletion logic forgets to update the prev pointer of the next node?

medium

A. The list will reverse automatically

B. The head pointer will always point to null

C. The deleted node will remain in memory forever

D. The list may become corrupted with dangling backward links

Solution

1. Step 1: Identify pointer updates needed on deletion

   When deleting a node, the previous node's next and the next node's prev pointers must be updated to bypass the deleted node.

2. Step 2: Consequence of missing prev update

   If the next node's prev pointer is not updated, it still points to the deleted node, causing backward links to be incorrect and list corruption.

3. Final Answer:

   The list may become corrupted with dangling backward links -> Option D

4. Quick Check:

   Missing prev update breaks backward links [OK]

Hint: Always update both prev and next pointers when deleting [OK]

Common Mistakes:

• Updating only next pointer
• Not breaking loop after deletion
• Forgetting to handle head or tail cases

5. You have a doubly linked list with nodes: 2 -> 4 -> 6 -> 4 -> 8 -> null. You want to delete all nodes with value 4 using a delete_by_value function that removes only the first matching node per call. How many times must you call delete_by_value(4) to remove all 4s, and what will the final list look like?

hard

A. Call once; final list: 2 -> 4 -> 6 -> 8 -> null

B. Call once; final list: 2 -> 6 -> 4 -> 8 -> null

C. Call twice; final list: 2 -> 6 -> 8 -> null

D. Call twice; final list: 2 -> 4 -> 6 -> 8 -> null

Solution

1. Step 1: Understand deletion per call

   Each call to delete_by_value(4) removes only the first node with value 4.

2. Step 2: Count how many 4s and calls needed

   There are two nodes with value 4. So, two calls are needed to remove both.

3. Step 3: Final list after deletions

   After two deletions, the list becomes 2 -> 6 -> 8 -> null.

4. Final Answer:

   Call twice; final list: 2 -> 6 -> 8 -> null -> Option C

5. Quick Check:

   Two 4s, two deletes, final list without 4s [OK]

Hint: Delete one node per call; repeat to remove all matches [OK]

Common Mistakes:

• Assuming one call removes all matching nodes
• Not updating pointers after each deletion
• Confusing node values or order