Insert at Middle Specific Position in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert a new node at position 3 in a singly linked list.

DSA C++

Node* insertAtPosition(Node* head, int data) {
    Node* newNode = new Node(data);
    Node* temp = head;
    int count = 1;
    while (count < [1] - 1 && temp != nullptr) {
        temp = temp->next;
        count++;
    }
    newNode->next = temp->next;
    temp->next = newNode;
    return head;
}

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

A3

B2

C4

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using the position directly without subtracting 1 causes incorrect insertion.

Not checking for nullptr before accessing next pointer.

To insert at position 3, we stop at position 2 (one before 3) to adjust pointers correctly.

2fill in blank

medium

Complete the code to handle insertion at position 1 (head) in the linked list.

DSA C++

Node* insertAtPosition(Node* head, int data, int position) {
    Node* newNode = new Node(data);
    if (position == [1]) {
        newNode->next = head;
        head = newNode;
        return head;
    }
    // code for other positions
    return head;
}

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A0

B-1

C2

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as position for head insertion in 1-based indexing.

Not updating head pointer after insertion.

Position 1 means inserting at the head of the list.

3fill in blank

hard

Fix the error in the loop condition to avoid null pointer dereference when inserting at a middle position.

DSA C++

while (temp != nullptr && temp->next != nullptr && count < [1] - 1) {
    temp = temp->next;
    count++;
}

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Aposition

Bdata

Chead

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names causing compilation errors.

Not checking for nullptr before accessing next.

The loop should run until one node before the target position.

4fill in blank

hard

Fill both blanks to correctly update pointers when inserting a new node at a given position.

DSA C++

newNode->next = [1];
[2]->next = newNode;

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Atemp->next

Bhead

Ctemp

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of pointer assignments causing list corruption.

Assigning newNode->next to wrong pointer.

First, newNode points to the next node after temp, then temp points to newNode.

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 C++

Node* insertAtPosition(Node* head, int data, int position) {
    Node* newNode = new Node(data);
    if (position == [1]) {
        newNode->next = head;
        head = newNode;
        return head;
    }
    Node* temp = head;
    int count = 1;
    while (count < [2] - 1 && temp != nullptr) {
        temp = temp->next;
        count++;
    }
    newNode->next = [3];
    temp->next = newNode;
    return head;
}

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

A1

Bposition

Ctemp->next

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Not handling head insertion separately.

Looping too far or not far enough.

Incorrect pointer assignments causing broken list.

Position 1 means insert at head. Loop runs until node before position. Then newNode points to temp->next.

Practice

1. What does inserting a node at a specific middle position in a linked list mean?

easy

A. Adding a new node only at the start of the list

B. Adding a new node exactly at the given position counting from the head

C. Adding a new node only at the end of the list

D. Replacing the node at the given position with a new node

Solution

1. Step 1: Understand insertion position

   Inserting at a specific middle position means placing the new node exactly at that position counting from the start (head) of the list.

2. Step 2: Differentiate from other insertions

   Insertion at start or end is different; here we insert in between nodes without replacing any node.

3. Final Answer:

   Adding a new node exactly at the given position counting from the head -> Option B

4. Quick Check:

   Insert at position means place new node there [OK]

Hint: Insert means add new node at exact position, not replace [OK]

Common Mistakes:

• Confusing insertion with replacement
• Thinking insertion only happens at start or end
• Ignoring position counting from head

2. Which of the following C++ code snippets correctly inserts a new node with value 10 at position 3 in a singly linked list?

easy

A. Node* temp = head; for(int i=1; i<2; i++) temp = temp->next; Node* newNode = new Node(10); newNode->next = temp->next; temp->next = newNode;

B. Node* newNode = new Node(10); newNode->next = head; head = newNode;

C. Node* temp = head; for(int i=1; i<3; i++) temp = temp->next; Node* newNode = new Node(10); newNode->next = temp->next; temp->next = newNode;

D. Node* newNode = new Node(10); head->next = newNode; newNode->next = NULL;

Solution

1. Step 1: Identify correct loop for position 3 insertion

   To insert at position 3, we stop at node 2 (position 2), so loop runs i=1 to i<2.

2. Step 2: Check pointer updates

   New node's next points to temp->next, then temp->next updated to new node. This correctly inserts at position 3.

3. Final Answer:

   Code snippet in option A correctly inserts at position 3 -> Option A

4. Quick Check:

   Loop stops at position before insertion [OK]

Hint: Loop till position-1, then insert new node [OK]

Common Mistakes:

• Looping one extra time causing wrong position
• Not updating newNode->next before temp->next
• Inserting at wrong position due to loop error

3. What will be the linked list after inserting value 15 at position 2 in the list: 5 -> 10 -> 20 -> null?

Node* head = new Node(5);
head->next = new Node(10);
head->next->next = new Node(20);

// Insert 15 at position 2
Node* temp = head;
for(int i=1; i<1; i++) temp = temp->next;
Node* newNode = new Node(15);
newNode->next = temp->next;
temp->next = newNode;

medium

A. 5 -> 15 -> 10 -> 20 -> null

B. 15 -> 5 -> 10 -> 20 -> null

C. 5 -> 10 -> 15 -> 20 -> null

D. 5 -> 10 -> 20 -> 15 -> null

Solution

1. Step 1: Trace loop to find insertion point

   Loop runs i=1 to i<1, so no iteration. temp points to head (value 5).

2. Step 2: Insert new node after temp

   New node 15 points to temp->next (10), then temp->next points to new node. List becomes 5 -> 15 -> 10 -> 20 -> null.

3. Final Answer:

   5 -> 15 -> 10 -> 20 -> null -> Option A

4. Quick Check:

   Insert after node 1 gives new node at position 2 [OK]

Hint: Loop zero times means insert after head [OK]

Common Mistakes:

• Miscounting loop iterations
• Inserting at wrong position
• Not updating pointers correctly

4. Identify the error in the following code that tries to insert a node with value 25 at position 4 in a linked list:

Node* temp = head;
for(int i=1; i<=4; i++) {
  temp = temp->next;
}
Node* newNode = new Node(25);
newNode->next = temp->next;
temp->next = newNode;

medium

A. No error, code works fine

B. New node's next pointer is not set correctly

C. New node is not created properly

D. Loop runs too many times causing temp to become NULL

Solution

1. Step 1: Analyze loop iterations

   Loop runs i=1 to i<=4 (4 times), moving temp 4 nodes ahead. For insertion at position 4, temp should stop at position 3.

2. Step 2: Consequence of loop error

   Temp moves too far, possibly NULL, causing runtime error when accessing temp->next.

3. Final Answer:

   Loop runs too many times causing temp to become NULL -> Option D

4. Quick Check:

   Loop must run position-2 times, not position times [OK]

Hint: Loop till position-2 to avoid NULL pointer [OK]

Common Mistakes:

• Using <= instead of < in loop condition
• Not checking for NULL before accessing next
• Incorrect loop range for insertion

5. Given a singly linked list with nodes: 1 -> 3 -> 5 -> 7 -> null, write the steps to insert a new node with value 4 at position 3. What will be the final list?

hard

A. 1 -> 4 -> 3 -> 5 -> 7 -> null

B. 4 -> 1 -> 3 -> 5 -> 7 -> null

C. 1 -> 3 -> 4 -> 5 -> 7 -> null

D. 1 -> 3 -> 5 -> 7 -> 4 -> null

Solution

1. Step 1: Traverse to node before position 3

   Start at head (1), move to next node (3) which is position 2. Stop here to insert after this node.

2. Step 2: Insert new node with value 4

   Create new node 4, set its next to current node's next (5), then update current node's next to new node.

3. Final Answer:

   1 -> 3 -> 4 -> 5 -> 7 -> null -> Option C

4. Quick Check:

   Insert at position 3 places new node between 3 and 5 [OK]

Hint: Stop at position-1 node, insert new node after it [OK]

Common Mistakes:

• Inserting at wrong position
• Not updating pointers correctly
• Confusing position counting from 0 or 1