Get Length of Linked List in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the length counter to zero.

DSA C++

int getLength(Node* head) {
    int length = [1];
    Node* current = head;
    while (current != nullptr) {
        length++;
        current = current->next;
    }
    return length;
}

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

Ahead

B1

Cnullptr

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting length at 1 instead of 0

Initializing length with head pointer

Using nullptr as initial length

The length counter should start at 0 before counting nodes.

2fill in blank

medium

Complete the code to move to the next node in the linked list.

DSA C++

int getLength(Node* head) {
    int length = 0;
    Node* current = head;
    while (current != nullptr) {
        length++;
        current = [1];
    }
    return length;
}

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

Ahead->next

Bcurrent->next

Ccurrent

Dnullptr

Attempts:

3 left

💡 Hint

Common Mistakes

Using head->next instead of current->next

Assigning current to itself causing infinite loop

Setting current to nullptr prematurely

To move forward, update current to current->next.

3fill in blank

hard

Fix the error in the while loop condition to correctly check the end of the list.

DSA C++

int getLength(Node* head) {
    int length = 0;
    Node* current = head;
    while ([1]) {
        length++;
        current = current->next;
    }
    return length;
}

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

Acurrent != nullptr

Bcurrent == nullptr

Chead != nullptr

Dhead == nullptr

Attempts:

3 left

💡 Hint

Common Mistakes

Using current == nullptr which ends loop immediately

Checking head instead of current in loop

Using incorrect null checks causing runtime errors

The loop should continue while current is not nullptr.

4fill in blank

hard

Complete the for loop to traverse the linked list and count its length.

DSA C++

int getLength(Node* head) {
    int length = 0;
    for (Node* current = head; [1]; [2]) {
        length++;
    }
    return length;
}

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

Acurrent != nullptr

Bcurrent = current->next

Chead != nullptr

Dcurrent = head->next

Attempts:

3 left

💡 Hint

Common Mistakes

Using head != nullptr in the condition instead of current

Incorrect update like current = head->next

Confusing while loop syntax with for loop

Use 'current != nullptr' as the loop condition and 'current = current->next' as the update expression.

5fill in blank

hard

Complete the recursive version of getLength by filling the base case condition, base case return value, and recursive call.

DSA C++

int getLength(Node* head) {
    if ([1]) {
        return [2];
    }
    return 1 + getLength([3]);
}

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

Ahead == nullptr

B0

Chead->next

Dhead != nullptr

Attempts:

3 left

💡 Hint

Common Mistakes

Using head != nullptr as base case condition

Returning 1 instead of 0 in base case

Recursive call on head instead of head->next causing infinite recursion

Base case: if (head == nullptr) return 0; Recursive case: return 1 + getLength(head->next);

Practice

1. What does the function getLength do when given the head of a linked list?

easy

A. Deletes the linked list

B. Returns the value of the first node

C. Returns the number of nodes in the linked list

D. Returns the last node of the linked list

Solution

1. Step 1: Understand the function purpose

   The function getLength counts nodes starting from the head until the end.

2. Step 2: Identify the output

   It returns the total count of nodes, which is the length of the linked list.

3. Final Answer:

   Returns the number of nodes in the linked list -> Option C

4. Quick Check:

   Counting nodes = length [OK]

Hint: Count nodes one by one until null [OK]

Common Mistakes:

• Confusing length with node value
• Trying to delete nodes instead of counting
• Returning the last node instead of count

2. Which of the following is the correct syntax to initialize a pointer to the head of a linked list in C++?

easy

A. Node* head = NULL;

B. Node head = NULL;

C. Node* head = 0;

D. Node head = 0;

Solution

1. Step 1: Understand pointer initialization

   In C++, a pointer to a node is declared as Node* and can be initialized to NULL or nullptr.

2. Step 2: Check each option

   Node* head = NULL; uses Node* head = NULL; which is correct pointer initialization syntax.

3. Final Answer:

   Node* head = NULL; -> Option A

4. Quick Check:

   Pointer declaration uses * and NULL [OK]

Hint: Use * for pointers and NULL for empty [OK]

Common Mistakes:

• Declaring pointer without *
• Assigning NULL to non-pointer variable
• Using 0 instead of NULL (less clear)

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

struct Node {
  int data;
  Node* next;
};

int getLength(Node* head) {
  int count = 0;
  while (head != NULL) {
    count++;
    head = head->next;
  }
  return count;
}

int main() {
  Node n3 = {30, NULL};
  Node n2 = {20, &n3};
  Node n1 = {10, &n2};
  int length = getLength(&n1);
  std::cout << length;
  return 0;
}

medium

A. 3

B. 2

C. 1

D. 0

Solution

1. Step 1: Trace the linked list nodes

   The list has nodes n1 -> n2 -> n3 -> NULL, so total 3 nodes.

2. Step 2: Count nodes in getLength

   The function counts each node until NULL, so count becomes 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   3 nodes counted = 3 [OK]

Hint: Count nodes by following next pointers until NULL [OK]

Common Mistakes:

• Counting only first node
• Off-by-one error in loop
• Confusing data values with count

4. Identify the error in the following code that tries to get the length of a linked list:

int getLength(Node* head) {
  int count = 0;
  while (head->next != NULL) {
    count++;
    head = head->next;
  }
  return count;
}

medium

A. It causes a segmentation fault

B. It misses counting the last node

C. It counts nodes twice

D. It returns the data of the last node

Solution

1. Step 1: Analyze the loop condition

   The loop runs while head->next != NULL, so it stops before the last node.

2. Step 2: Check counting logic

   Since last node is not counted, the returned count is one less than actual length.

3. Final Answer:

   It misses counting the last node -> Option B

4. Quick Check:

   Loop condition excludes last node [OK]

Hint: Use while(head != NULL) to count all nodes [OK]

Common Mistakes:

• Using head->next in loop condition
• Not counting last node
• Confusing node data with count

5. Given a linked list where each node contains an integer, how would you modify the getLength function to return the length only if all node values are positive? If any node has zero or negative value, return -1.

hard

A. Count nodes normally and ignore values

B. Return -1 if list is empty, else return length

C. Return length only if first node is positive

D. Traverse nodes, if value <= 0 return -1, else count nodes and return count

Solution

1. Step 1: Traverse each node checking value

   While moving through the list, check if node's data is <= 0; if yes, return -1 immediately.

2. Step 2: Count nodes if all values positive

   If all nodes have positive values, count them and return the count as length.

3. Final Answer:

   Traverse nodes, if value <= 0 return -1, else count nodes and return count -> Option D

4. Quick Check:

   Check values during count, return -1 if any non-positive [OK]

Hint: Check values while counting, stop early if non-positive [OK]

Common Mistakes:

• Ignoring node values during count
• Checking only first node value
• Returning length even if negative values exist