Get Length of Linked List in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the length variable to zero.

DSA Java

int length = [1];

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

A0

Bnull

C-1

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing length to 1 instead of 0

Using null for an int variable

We start counting length from zero because the list is initially empty.

2fill in blank

medium

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

DSA Java

current = current.[1];

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

Aprev

Bnext

Cchild

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is for doubly linked lists

Using unrelated field names

In a singly linked list, each node points to the next node using the 'next' reference.

3fill in blank

hard

Fix the error in the loop condition to correctly traverse the linked list.

DSA Java

while (current [1] null) {
    length++;
    current = current.next;
}

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

A==

B=

C!=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of '!='

Using '==' which stops immediately

Using '>' which is invalid for objects

The loop should continue while current is not null to visit all nodes.

4fill in blank

hard

Fill both blanks to create a method that returns the length of the linked list.

DSA Java

public int getLength(Node [1]) {
    int length = 0;
    Node current = [2];
    while (current != null) {
        length++;
        current = current.next;
    }
    return length;
}

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

Ahead

Btail

Cnode

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for parameter and current node

Using 'tail' which is the end of the list

The method parameter and the starting node variable should both be named 'head' to represent the start of the list.

5fill in blank

hard

Fill all three blanks to create a method that returns the length of the linked list using a for loop.

DSA Java

public int getLength(Node [1]) {
    int length = 0;
    for (Node [2] = [3]; [2] != null; [2] = [2].next) {
        length++;
    }
    return length;
}

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

Ahead

Bcurrent

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent variable names

Starting loop variable from wrong node

The parameter is 'head', the loop variable is 'current', and it starts from 'head'.

Practice

1. What does the length of a linked list represent?

easy

A. The sum of all node values

B. The value of the first node

C. The memory size of the linked list

D. The number of nodes in the linked list

Solution

1. Step 1: Understand linked list structure

   A linked list is made of nodes connected one after another.

2. Step 2: Define length meaning

   The length is how many nodes are present in the list.

3. Final Answer:

   The number of nodes in the linked list -> Option D

4. Quick Check:

   Length = count of nodes [OK]

Hint: Length counts nodes, not values or memory [OK]

Common Mistakes:

• Confusing length with sum of values
• Thinking length is memory size
• Using first node value as length

2. Which of the following Java code snippets correctly initializes a variable to count the length of a linked list named head?

easy

A. int length = head; Node current = 0;

B. int length = 0; Node current = head;

C. Node length = 0; int current = head;

D. int length = null; Node current = head;

Solution

1. Step 1: Identify correct variable types

   Length should be an integer starting at 0; current should be a Node starting at head.

2. Step 2: Check each option

   int length = 0; Node current = head; correctly declares int length = 0; and Node current = head;. Others mix types or assign invalid values.

3. Final Answer:

   int length = 0; Node current = head; -> Option B

4. Quick Check:

   Initialize count as int 0 and pointer as Node head [OK]

Hint: Count is int zero; pointer is Node starting at head [OK]

Common Mistakes:

• Mixing variable types
• Assigning head to int
• Using null for int variable

3. What is the output of the following Java code snippet?

class Node {
  int data;
  Node next;
  Node(int d) { data = d; next = null; }
}

public class Test {
  public static int getLength(Node head) {
    int count = 0;
    Node current = head;
    while (current != null) {
      count++;
      current = current.next;
    }
    return count;
  }

  public static void main(String[] args) {
    Node n1 = new Node(5);
    Node n2 = new Node(10);
    Node n3 = new Node(15);
    n1.next = n2;
    n2.next = n3;
    System.out.println(getLength(n1));
  }
}

medium

A. 0

B. 2

C. 3

D. NullPointerException

Solution

1. Step 1: Trace linked list nodes

   Nodes are n1 -> n2 -> n3, so total 3 nodes linked.

2. Step 2: Count nodes in getLength

   Loop increments count for each node until current is null, so count = 3.

3. Final Answer:

   3 -> Option C

4. Quick Check:

   3 nodes counted in list [OK]

Hint: Count increments once per node until null [OK]

Common Mistakes:

• Counting nodes incorrectly
• Expecting 0 for non-empty list
• Confusing null pointer errors

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

public int getLength(Node head) {
  int count = 0;
  while (head.next != null) {
    count++;
    head = head.next;
  }
  return count;
}

medium

A. It does not count the last node

B. It causes infinite loop

C. It throws NullPointerException immediately

D. It counts nodes twice

Solution

1. Step 1: Analyze loop condition

   The loop runs while head.next != null, so it stops before last node.

2. Step 2: Check counting logic

   Since last node's next is null, it is never counted, so count misses last node.

3. Final Answer:

   It does not count the last node -> Option A

4. Quick Check:

   Loop condition excludes last node [OK]

Hint: Loop on current != null to count all nodes [OK]

Common Mistakes:

• Using head.next != null instead of head != null
• Missing last node count
• Confusing loop conditions

5. Given a linked list where each node contains an integer, write a method to find the length of the list but only count nodes with even values. Which approach is correct?

hard

A. Traverse all nodes, increment count only if node's data % 2 == 0

B. Count nodes until first odd value is found

C. Count all nodes and then subtract odd nodes count

D. Only count nodes if next node is even

Solution

1. Step 1: Understand problem requirement

   We must count nodes with even values only, ignoring odd nodes.

2. Step 2: Choose correct counting method

   Traverse entire list, check each node's data; increment count if even (data % 2 == 0).

3. Final Answer:

   Traverse all nodes, increment count only if node's data % 2 == 0 -> Option A

4. Quick Check:

   Count even nodes by checking each node [OK]

Hint: Check each node's value; count only if even [OK]

Common Mistakes:

• Stopping count at first odd node
• Subtracting odd count after full count
• Checking next node's value instead of current