Insert at End of Doubly Linked List in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node with the given data.

DSA Go

newNode := &Node{data: [1], next: nil, prev: nil}

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Avalue

Bdata

Cd

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name not defined in the function.

Using 'data' instead of the parameter name.

The variable 'd' holds the data to insert, so it should be assigned to the new node's data field.

2fill in blank

medium

Complete the code to check if the list is empty.

DSA Go

if head == [1] {

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Aempty

Bnull

C0

Dnil

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'null' which is not valid in Go.

Using 0 or 'empty' which are not pointer values.

In Go, 'nil' is used to check if a pointer is empty or not initialized.

3fill in blank

hard

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

DSA Go

for current.[1] != nil {
    current = current.next
}

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Anext

BnextNode

Cprev

Dpointer

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which moves backward in the list.

Using undefined fields like 'nextNode' or 'pointer'.

To move forward in the list, we check and use the 'next' pointer of the current node.

4fill in blank

hard

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

DSA Go

current.next = [1]
[2].prev = current

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AnewNode

Cnode

Dnewnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for the new node.

Forgetting to set the prev pointer of the new node.

The new node is assigned to current.next, and its prev pointer is set to current.

5fill in blank

hard

Fill all three blanks to return the head of the updated list.

DSA Go

if head == nil {
    head = [1]
    return [2]
}

return [3]

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AnewNode

Bhead

Cnewnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent variable names for the new node.

Returning the new node instead of head when list is not empty.

When the list is empty, head is set to newNode and returned. Otherwise, the original head is returned.

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 structure of a doubly linked list

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

2. Step 2: Identify the effect of inserting at the end

   Inserting at the end means adding a new node after the current last node, updating pointers accordingly.

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 reverses the list
• Assuming insertion happens at the start

2. Which of the following Go code snippets correctly updates the 'next' pointer when inserting a new node at the end of a doubly linked list?

easy

A. newNode.next = last

B. newNode.prev = last.next

C. last.next = newNode

D. last.prev = newNode

Solution

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

   When inserting at the end, the last node's next pointer should point to the new node.

2. Step 2: Match correct pointer assignment

   Setting last.next = newNode correctly links the last node to the new node.

3. Final Answer:

   last.next = newNode -> Option C

4. Quick Check:

   last.next points to new node [OK]

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

Common Mistakes:

• Assigning newNode.prev to last.next incorrectly
• Setting newNode.next to last (wrong direction)
• Changing last.prev instead of last.next

3. What will be the printed output of the doubly linked list after inserting nodes with values 10, 20, and 30 at the end in order? Assume the print function shows values from head to tail.

medium

A. null <-> 10 <-> 20 <-> 30

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

C. 10 <-> 30 <-> 20 <-> null

D. 10 <-> 20 <-> 30 <-> null

Solution

1. Step 1: Insert 10 at end when list is empty

   List becomes: 10 -> null

2. Step 2: Insert 20 at end

   List becomes: 10 <-> 20 -> null

3. Step 3: Insert 30 at end

   List becomes: 10 <-> 20 <-> 30 -> null

4. Final Answer:

   10 <-> 20 <-> 30 <-> null -> Option D

5. Quick Check:

   Insert order preserved from head to tail [OK]

Hint: Insertion at end keeps order as inserted [OK]

Common Mistakes:

• Assuming insertion reverses order
• Printing null at start instead of end
• Mixing node order in output

4. Given the following Go code snippet for inserting at the end of a doubly linked list, what is the error?

func InsertEnd(head *Node, data int) *Node {
    newNode := &Node{data: data}
    if head == nil {
        head = newNode
    } else {
        temp := head
        for temp.next != nil {
            temp = temp.next
        }
        temp.next = newNode
        newNode.prev = temp
    }
    return head
}

medium

A. The newNode's prev pointer is incorrectly assigned

B. The newNode's next pointer is not set to nil

C. The loop condition should be temp.prev != nil

D. The function does not update the head when list is empty

Solution

1. Step 1: Check newNode pointer initialization

   In Go, uninitialized pointers default to nil, but explicitly setting newNode.next = nil is safer.

2. Step 2: Identify missing explicit next pointer assignment

   The code does not set newNode.next = nil, which can cause issues if newNode is reused or inspected.

3. Final Answer:

   The newNode's next pointer is not set to nil -> Option B

4. Quick Check:

   Always set newNode.next = nil at insertion [OK]

Hint: Always set newNode.next = nil when inserting at end [OK]

Common Mistakes:

• Ignoring explicit nil assignment for newNode.next
• Confusing prev and next pointers
• Incorrect loop condition for traversal

5. You have a doubly linked list with nodes 5 <-> 15 <-> 25. You want to insert a new node with value 35 at the end. After insertion, which pointers must be updated to maintain list integrity?

hard

A. Set last node's next to new node, new node's prev to last node, new node's next to nil

B. Set new node's next to last node, last node's prev to new node

C. Set head's prev to new node, new node's next to head

D. Set new node's prev and next to nil only

Solution

1. Step 1: Identify the last node before insertion

   The last node is the one with value 25.

2. Step 2: Update pointers to insert new node at end

   Set last node's next to new node, new node's prev to last node, and new node's next to nil to mark end.

3. Final Answer:

   Set last node's next to new node, new node's prev to last node, new node's next to nil -> Option A

4. Quick Check:

   Last.next = new, new.prev = last, new.next = nil [OK]

Hint: Update last.next, new.prev, and new.next for end insertion [OK]

Common Mistakes:

• Reversing prev and next pointers
• Not setting new node's next to nil
• Changing head pointers incorrectly