Linked List vs Array When to Choose Which in DSA Java - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Java

int[] numbers = new int[[1]];

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

A0

B5

C10

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as size which creates an empty array.

Using 1 or 10 which does not match the required size.

The array size is set to 5, so it can hold 5 integers indexed from 0 to 4.

2fill in blank

medium

Complete the code to add a new node with value 10 at the start of a linked list.

DSA Java

Node newNode = new Node([1]);
newNode.next = head;
head = newNode;

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

A10

Bhead

Cnull

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using null or head as the value instead of 10.

Confusing the value with the next pointer.

We create a new node with value 10 and link it to the current head, then update head to newNode.

3fill in blank

hard

Fix the error in the code to access the third element in an array named arr.

DSA Java

int thirdElement = arr[[1]];

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

A3

B1

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 3 which is the fourth element.

Using index 1 which is the second element.

Array indices start at 0, so the third element is at index 2.

4fill in blank

hard

Fill both blanks to iterate over a linked list and print each node's value.

DSA Java

Node current = head;
while (current [1] null) {
    System.out.println(current.[2]);
    current = current.next;
}

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

A!=

B==

Cvalue

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '!=' in the loop condition.

Printing current.next instead of current.value.

We loop while current is not null and print the current node's value.

5fill in blank

hard

Fill all three blanks to create a list of squares for numbers 1 to 5 using an array.

DSA Java

int[] squares = new int[5];
for (int i = 0; i [1] 5; i[2]) {
    squares[i] = (i [3] 1) * (i [3] 1);
}

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

A<

B++

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using i <= 5 which causes index out of bounds.

Using i-- which decreases i and causes infinite loop.

Using i - 1 instead of i + 1 for correct squares.

The loop runs while i < 5, increments i by 1 each time, and squares (i + 1).

Practice

1. Which data structure is better when you need fast random access to elements by index?

easy

A. Linked List

B. Array

C. Stack

D. Queue

Solution

1. Step 1: Understand random access requirement

   Random access means accessing any element directly by its position quickly.

2. Step 2: Compare Array and Linked List access times

   Arrays allow direct access by index in constant time, while linked lists require traversal.

3. Final Answer:

   Array -> Option B

4. Quick Check:

   Random access = Array [OK]

Hint: Arrays provide fast index access, linked lists do not [OK]

Common Mistakes:

• Thinking linked lists allow fast random access
• Confusing stack or queue with arrays
• Ignoring access time differences

2. Which of the following is the correct way to declare an array of integers in Java?

easy

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

B. int arr = new int[5];

C. int arr[] = new int();

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

Solution

1. Step 1: Recall Java array declaration syntax

   In Java, arrays are declared with type[], variable name, and size with new keyword.

2. Step 2: Check each option for syntax correctness

   int[] arr = new int[5]; matches correct syntax: int[] arr = new int[5]; others have errors.

3. Final Answer:

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

4. Quick Check:

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

Hint: Remember Java arrays use type[] name = new type[size]; [OK]

Common Mistakes:

• Missing brackets [] after type
• Using parentheses instead of brackets
• Wrong keyword 'array' instead of type

3. Consider this Java code using a linked list:

LinkedList<Integer> list = new LinkedList<>();
list.add(10);
list.add(20);
list.add(30);
System.out.println(list.get(1));

What will be the output?

medium

A. 10

B. 30

C. IndexOutOfBoundsException

D. 20

Solution

1. Step 1: Understand list contents after adds

   Elements added in order: 10 at index 0, 20 at index 1, 30 at index 2.

2. Step 2: Identify element at index 1

   list.get(1) returns the element at index 1, which is 20.

3. Final Answer:

   20 -> Option D

4. Quick Check:

   list.get(1) = 20 [OK]

Hint: Indexing starts at 0; second element is index 1 [OK]

Common Mistakes:

• Assuming index starts at 1
• Confusing add order with index
• Expecting runtime error incorrectly

4. The following Java code tries to remove an element from an array but causes an error:

int[] arr = {1, 2, 3, 4};
arr.remove(2);

What is the main issue here?

medium

A. Arrays do not have a remove method

B. Index 2 is out of bounds

C. Array elements cannot be integers

D. Syntax error in array declaration

Solution

1. Step 1: Check if arrays support remove method

   Java arrays have fixed size and do not support remove method.

2. Step 2: Identify correct way to remove elements

   To remove elements, use ArrayList or create a new array without the element.

3. Final Answer:

   Arrays do not have a remove method -> Option A

4. Quick Check:

   Arrays fixed size = no remove method [OK]

Hint: Arrays fixed size, no remove method; use ArrayList [OK]

Common Mistakes:

• Thinking arrays support remove like lists
• Assuming index 2 is invalid
• Confusing syntax errors with method errors

5. You need to frequently insert and delete elements in the middle of a large collection. Which data structure is more efficient and why?

hard

A. Array, because it uses less memory

B. Linked List, because it uses contiguous memory

C. Linked List, because it allows fast insertions and deletions without shifting elements

D. Array, because it supports random access

Solution

1. Step 1: Analyze insertion and deletion costs

   Arrays require shifting elements for insert/delete in middle, which is slow for large data.

2. Step 2: Understand linked list advantages

   Linked lists use nodes with pointers, so insert/delete in middle is fast without shifting.

3. Final Answer:

   Linked List, because it allows fast insertions and deletions without shifting elements -> Option C

4. Quick Check:

   Fast middle insert/delete = Linked List [OK]

Hint: Linked lists excel at middle insert/delete without shifting [OK]

Common Mistakes:

• Choosing array for frequent middle insert/delete
• Confusing memory layout of linked lists
• Ignoring shifting cost in arrays