Memory Layout Comparison Array vs Linked List in DSA Java - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of integers with size 5.

DSA Java

int[] numbers = new int[1];

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

A[5]

B{5}

C(5)

D<5>

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of square brackets for array size.

The correct syntax to declare an array of size 5 in Java is using square brackets with the size inside: new int[5].

2fill in blank

medium

Complete the code to create a new node for a singly linked list with value 10.

DSA Java

Node node = new Node([1]);

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

Anode

B"10"

C10

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using string "10" instead of integer 10.

The node value should be an integer 10, not a string or null.

3fill in blank

hard

Fix the error in the code to link two nodes in a singly linked list.

DSA Java

node1.[1] = node2;

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

Apointer

Bprev

Clink

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using prev or other incorrect field names.

The correct field to link nodes in a singly linked list is next.

4fill in blank

hard

Fill both blanks to create an array and access its third element.

DSA Java

int[] arr = new int[1];
int value = arr[2];

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

A[5]

B[2]

C(2)

D(5)

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of square brackets.

Using wrong index for third element.

The array is created with size 5 using [5]. The third element is at index 2, accessed with [2].

5fill in blank

hard

Fill all three blanks to create a linked list node, assign value 7, and link to null.

DSA Java

Node node = new Node([1]);
node.[2] = [3];

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

A7

Bnext

Cnull

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect field name instead of next.

Assigning value instead of null to next.

Create a node with value 7, set its next pointer to null to mark the end of the list.

Practice

1. Which of the following best describes the memory layout of an array compared to a linked list?

easy

A. Array elements are stored in contiguous memory locations, while linked list nodes are scattered in memory.

B. Array elements are scattered in memory, while linked list nodes are stored contiguously.

C. Both array and linked list nodes are stored contiguously in memory.

D. Both array and linked list nodes are scattered randomly in memory.

Solution

1. Step 1: Understand array memory layout

   Arrays store elements in contiguous blocks of memory, meaning all elements are next to each other.

2. Step 2: Understand linked list memory layout

   Linked list nodes are allocated separately and linked by pointers, so they can be scattered anywhere in memory.

3. Final Answer:

   Array elements are stored in contiguous memory locations, while linked list nodes are scattered in memory. -> Option A

4. Quick Check:

   Array = contiguous, Linked List = scattered [OK]

Hint: Arrays use continuous memory; linked lists use scattered nodes [OK]

Common Mistakes:

• Thinking linked list nodes are stored contiguously
• Confusing array with linked list memory layout
• Assuming both have same memory layout

2. Which Java syntax correctly declares an array of integers with size 5?

easy

A. int[] arr = new int(5);

B. int arr = new int[5];

C. int arr[] = new int[5];

D. int[] arr = int[5];

Solution

1. Step 1: Recall correct array declaration syntax in Java

   Arrays are declared with square brackets after type or variable name and initialized with 'new' and size in square brackets.

2. Step 2: Check each option

   int arr[] = new int[5]; uses correct syntax: int arr[] = new int[5]; Options A, C, and D have syntax errors.

3. Final Answer:

   int arr[] = new int[5]; -> Option C

4. Quick Check:

   Correct Java array syntax = int arr[] = new int[5]; [OK]

Hint: Use square brackets [] with new keyword for arrays [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Missing 'new' keyword
• Assigning array size without new keyword

3. Consider the following Java code that creates a linked list node and an array element:

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

public class Test {
  public static void main(String[] args) {
    int[] arr = new int[3];
    arr[0] = 10;
    Node n = new Node(10);
    System.out.println(arr[0] + ", " + n.data);
  }
}

What is the output?

medium

A. 0, 10

B. 10, 10

C. 10, 0

D. Compilation error

Solution

1. Step 1: Trace array initialization and assignment

   Array of size 3 is created; arr[0] is assigned 10.

2. Step 2: Trace linked list node creation

   Node n is created with data = 10.

3. Step 3: Print values

   Prints arr[0] (10) and n.data (10) separated by comma.

4. Final Answer:

   10, 10 -> Option B

5. Quick Check:

   arr[0] = 10 and node data = 10 [OK]

Hint: Check assigned values, both are 10 here [OK]

Common Mistakes:

• Assuming default array values instead of assigned
• Confusing node data initialization
• Expecting compilation error

4. The following Java code attempts to traverse a linked list but causes a runtime error:

Node head = null;
head.next = new Node(5);

What is the cause of the error?

medium

A. Syntax error in assignment

B. Node class is not defined

C. Cannot assign new Node to next without constructor

D. head is null, so accessing head.next causes NullPointerException

Solution

1. Step 1: Analyze head initialization

   head is set to null, meaning it points to nothing.

2. Step 2: Accessing head.next causes error

   Trying to access next on null causes NullPointerException at runtime.

3. Final Answer:

   head is null, so accessing head.next causes NullPointerException -> Option D

4. Quick Check:

   Null reference access causes NullPointerException [OK]

Hint: Null object cannot access members; causes NullPointerException [OK]

Common Mistakes:

• Thinking it's a syntax error
• Assuming Node class missing
• Ignoring null initialization

5. You want to insert 1000 elements and frequently add or remove elements in the middle. Considering memory layout, which data structure is more efficient and why?

hard

A. Linked list, because scattered nodes allow efficient insertion and deletion without shifting elements

B. Array, because it uses less memory than linked list nodes

C. Array, because contiguous memory improves insertion speed in the middle

D. Linked list, because it stores elements contiguously for faster access

Solution

1. Step 1: Understand insertion cost in arrays

   Arrays require shifting elements after insertion in the middle, which is costly.

2. Step 2: Understand linked list insertion

   Linked lists insert by changing pointers, no shifting needed, so insertion/deletion is efficient.

3. Step 3: Consider memory layout impact

   Linked list nodes are scattered but allow flexible insertion; arrays are contiguous but costly to modify in middle.

4. Final Answer:

   Linked list, because scattered nodes allow efficient insertion and deletion without shifting elements -> Option A

5. Quick Check:

   Linked list better for frequent middle insertions [OK]

Hint: Linked list avoids shifting; better for frequent middle changes [OK]

Common Mistakes:

• Choosing array for faster insertion in middle
• Ignoring shifting cost in arrays
• Confusing memory layout with access speed