Insert at Middle Specific Position in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a new node at the given position in the linked list.

DSA Python

new_node.next = current[1]

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

A.prev

B.next.next

C.next

D.prev.next

Attempts:

3 left

💡 Hint

Common Mistakes

Using .prev instead of .next causes incorrect linking.

Skipping the next pointer leads to broken list connections.

The new node's next pointer should point to the current node's next node to insert correctly.

2fill in blank

medium

Complete the code to move to the node just before the insertion position.

DSA Python

for _ in range([1] - 1):
    current = current.next

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

Aposition

Bpos

Cindex

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using an undefined variable like 'index' or 'count'.

Looping the wrong number of times.

We use the variable 'position' to represent the target insertion index.

3fill in blank

hard

Fix the error in the insertion code to correctly update the current node's next pointer.

DSA Python

current.next = [1]

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

Anew_node

Bnew_node.next

Ccurrent

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning current.next to new_node.next breaks the link.

Assigning current.next to None removes the rest of the list.

The current node's next should point to the new node to insert it properly.

4fill in blank

hard

Fill both blanks to complete the insertion logic inside the linked list.

DSA Python

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

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

A.next

B.prev

C.next.next

D.prev.next

Attempts:

3 left

💡 Hint

Common Mistakes

Using '.prev' breaks the forward link.

Mixing '.next' and '.prev' causes errors.

First, new_node.next points to current.next, then current.next points to new_node.

5fill in blank

hard

Fill all three blanks to create a function that inserts a node at a specific position in a singly linked list.

DSA Python

def insert_at_position(head, data, position):
    new_node = Node(data)
    if position == 0:
        new_node.next = head
        return new_node
    current = head
    for _ in range([1] - 1):
        current = current.next
    new_node.next = current[2]
    current[3] = new_node
    return head

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

Aposition

B.next

D.prev

Attempts:

3 left

💡 Hint

Common Mistakes

Using '.prev' instead of '.next' breaks the list.

Incorrect loop variable causes wrong insertion point.

The loop uses 'position' to reach the node before insertion. Then new_node.next points to current.next, and current.next points to new_node.

Practice

1. What does it mean to insert an element at a specific middle position in a list?

easy

A. Add the element exactly at the given index, shifting others right

B. Replace the element at the given index with the new element

C. Add the element only if the list is empty

D. Add the element at the end of the list regardless of position

Solution

1. Step 1: Understand list insertion

   Inserting at a specific position means placing the new element at that index and moving existing elements to the right.

2. Step 2: Differentiate from replacement

   Replacing overwrites the element, but insertion shifts elements to keep all.

3. Final Answer:

   Add the element exactly at the given index, shifting others right -> Option A

4. Quick Check:

   Insert means add and shift, not replace or append [OK]

Hint: Insert shifts elements right at the given index [OK]

Common Mistakes:

• Confusing insert with replace
• Thinking insert always adds at end
• Assuming insert only works on empty lists

2. Which of the following is the correct syntax to insert the value 10 at index 2 in a Python list named lst?

easy

A. lst.append(2, 10)

B. lst.insert(2, 10)

C. lst.add(2, 10)

D. lst[2] = 10

Solution

1. Step 1: Recall Python list insertion method

   Python lists use the insert(index, value) method to add an element at a specific position.

2. Step 2: Check other options

   add is not a list method, append adds only at the end, and lst[2] = 10 replaces the element at index 2.

3. Final Answer:

   lst.insert(2, 10) -> Option B

4. Quick Check:

   Use insert(index, value) to add at position [OK]

Hint: Use insert(index, value) to add at any position [OK]

Common Mistakes:

• Using append to insert in middle
• Trying to assign with lst[2] = 10 instead of insert
• Using non-existent add method

3. What will be the output of the following code?

lst = [1, 2, 4, 5]
lst.insert(2, 3)
print(lst)

medium

A. [1, 2, 3, 4, 5]

B. [1, 2, 4, 3, 5]

C. [3, 1, 2, 4, 5]

D. [1, 2, 4, 5, 3]

Solution

1. Step 1: Understand insert at index 2

   Index 2 means the third position (0-based). Inserting 3 here shifts 4 and 5 right.

2. Step 2: Visualize the list after insertion

   List becomes [1, 2, 3, 4, 5] after insertion.

3. Final Answer:

   [1, 2, 3, 4, 5] -> Option A

4. Quick Check:

   Insert at index 2 places 3 before 4 [OK]

Hint: Index 2 means third position, insert shifts right [OK]

Common Mistakes:

• Inserting after index instead of at index
• Confusing insert with replace
• Miscounting zero-based index

4. Find the error in the following code that tries to insert 99 at index 3:

lst = [10, 20, 30]
lst.insert(4, 99)
print(lst)

medium

A. Index 4 is out of range, causes error

B. insert method requires two arguments

C. No error; 99 is added at the end

D. lst should be converted to a set before insert

Solution

1. Step 1: Check index validity for insert

   Python's insert allows index beyond list length; it adds element at the end.

2. Step 2: Confirm behavior of insert with large index

   Since index 4 > length 3, 99 is appended at the end without error.

3. Final Answer:

   No error; 99 is added at the end -> Option C

4. Quick Check:

   Insert with large index appends at end [OK]

Hint: Insert with index > length appends at end [OK]

Common Mistakes:

• Assuming index out of range causes error
• Confusing insert with assignment
• Thinking list must be converted to set

5. Given a list lst = [5, 10, 15, 20, 25], write code to insert the value 12 exactly in the middle of the list. What will be the list after insertion?

hard

A. [5, 10, 15, 12, 20, 25]

B. [12, 5, 10, 15, 20, 25]

C. [5, 12, 10, 15, 20, 25]

D. [5, 10, 12, 15, 20, 25]

Solution

1. Step 1: Calculate middle index of the list

   List length is 5, middle index is length // 2 = 2.

2. Step 2: Insert 12 at index 2

   Using lst.insert(2, 12) places 12 between 10 and 15.

3. Final Answer:

   [5, 10, 12, 15, 20, 25] -> Option D

4. Quick Check:

   Middle index = 2, insert shifts elements right [OK]

Hint: Middle index = length // 2, insert there [OK]

Common Mistakes:

• Inserting at wrong index (like 3)
• Replacing element instead of inserting
• Not calculating middle index correctly