Merge Two Sorted Linked Lists in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Python

class Node:
    def __init__(self, val):
        self.val = val
        self.next = [1]

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

Aval

B0

CNone

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to 0 or val instead of None.

Confusing next with the node's value.

When creating a new node, its next pointer should initially be None because it doesn't point to any other node yet.

2fill in blank

medium

Complete the code to start merging by creating a dummy node.

DSA Python

def mergeTwoLists(l1, l2):
    dummy = Node([1])
    current = dummy
    # merging logic follows

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

A-1

BNone

Cl1.val

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using None as a value which causes errors.

Using l1.val which may not exist if l1 is None.

A dummy node with a placeholder value like -1 helps simplify the merge logic without affecting the final list.

3fill in blank

hard

Fix the error in the while loop condition to merge until one list ends.

DSA Python

while l1 [1] None and l2 != None:
    if l1.val < l2.val:
        current.next = l1
        l1 = l1.next
    else:
        current.next = l2
        l2 = l2.next
    current = current.next

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

A==

B!=

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which stops the loop immediately.

Using comparison operators like '<' or '>' which are invalid here.

The loop should continue while both l1 and l2 are not None, so the condition uses '!=' to check they exist.

4fill in blank

hard

Fill both blanks to attach the remaining nodes after the loop ends.

DSA Python

if l1 [1] None:
    current.next = l1
else:
    current.next = [2]

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

Ais not

Bis

Cl2

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'is' instead of 'is not' in the if condition.

Attaching None instead of the remaining list.

If l1 still has nodes (is not None), attach it; otherwise attach l2.

5fill in blank

hard

Fill the blanks to return the merged list skipping the dummy node.

DSA Python

def mergeTwoLists(l1, l2):
    dummy = Node(-1)
    current = dummy
    while l1 != None and l2 != None:
        if l1.val < l2.val:
            current.next = l1
            l1 = l1.next
        else:
            current.next = l2
            l2 = l2.next
        current = current.next
    if l1 is not None:
        current.next = l1
    else:
        current.next = l2
    return [1].[2]

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

Adummy

Bnext

Chead

Dcurrent

Attempts:

3 left

💡 Hint

Common Mistakes

Returning dummy instead of dummy.next.

Returning current or head which are not defined here.

Return dummy.next to skip the dummy node and get the head of the merged list.