Stack Using Linked List vs Array Stack Trade-offs in DSA Java - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto an array-based stack.

DSA Java

stack[top] = element; top[1]=1;

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

A*

B-

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' causes overwriting previous elements.

We add 1 to the top index after placing the element to move the top pointer up.

2fill in blank

medium

Complete the code to pop an element from a linked list stack.

DSA Java

Node temp = top; top = top.[1]; return temp.data;

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

Aprev

Bchild

Cparent

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' causes errors because stack nodes link forward, not backward.

In a linked list stack, the top points to the latest node. We move top to the next node after popping.

3fill in blank

hard

Fix the error in checking if the array stack is full.

DSA Java

if (top [1] stack.length) { throw new StackOverflowError(); }

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

A>=

B>

C<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' misses the case when top equals length, causing overflow.

The top index equals the stack length when the stack is full, so '>=' is correct.

4fill in blank

hard

Fill both blanks to complete the linked list stack push method.

DSA Java

Node newNode = new Node(element); newNode.[1] = top; top = [2];

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

Anext

Bprev

Ctop

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' breaks the link direction.

Assigning top incorrectly causes stack corruption.

The new node's next points to the current top, then top is updated to the new node.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that filters stack elements greater than 10.

DSA Java

Map<Integer, Integer> filtered = stackElements.entrySet().stream().filter(e -> e.getValue() [1] 10).collect(Collectors.toMap(e -> e.[2], e -> e.[3]));

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

A>

BgetKey()

CgetValue()

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' filters wrong elements.

Mixing getKey() and getValue() causes wrong map construction.

We filter entries with values greater than 10, then collect keys and values properly.

Practice

1. Which of the following is a key advantage of using a linked list to implement a stack compared to using an array?

easy

A. Accessing elements by index is faster.

B. Memory usage is always less than an array.

C. The stack size can grow dynamically without a fixed limit.

D. It uses less memory overhead per element.

Solution

1. Step 1: Understand stack size behavior in linked list

   A linked list stack can grow dynamically as nodes are added, limited only by available memory.

2. Step 2: Compare with array stack size

   An array stack has a fixed size or requires resizing, which can be costly and limits immediate growth.

3. Final Answer:

   The stack size can grow dynamically without a fixed limit. -> Option C

4. Quick Check:

   Dynamic size = B [OK]

Hint: Linked list stacks grow dynamically; arrays have fixed size [OK]

Common Mistakes:

• Thinking array stacks grow dynamically without resizing
• Assuming linked list uses less memory always
• Confusing access speed advantages

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

easy

A. int stack = new int[10];

B. int[] stack = new int[10];

C. int[] stack = int[10];

D. int stack[] = int(10);

Solution

1. Step 1: Recall Java array declaration syntax

   In Java, arrays are declared with type[], variable = new type[size];

2. Step 2: Check each option

   int[] stack = new int[10]; matches correct syntax: int[] stack = new int[10]; others have syntax errors.

3. Final Answer:

   int[] stack = new int[10]; -> Option B

4. Quick Check:

   Correct Java array syntax = A [OK]

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

Common Mistakes:

• Missing 'new' keyword
• Using parentheses instead of brackets
• Declaring array without []

3. Consider the following Java code implementing a stack using a linked list. What will be printed after pushing 10, 20, then popping once?

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

class Stack {
  Node top;
  void push(int x) {
    Node n = new Node(x);
    n.next = top;
    top = n;
  }
  int pop() {
    if (top == null) return -1;
    int val = top.data;
    top = top.next;
    return val;
  }
}

public class Main {
  public static void main(String[] args) {
    Stack s = new Stack();
    s.push(10);
    s.push(20);
    System.out.println(s.pop());
  }
}

medium

A. 20

B. null

C. 10

D. Compilation error

Solution

1. Step 1: Trace push operations

   Push 10: top points to node with 10. Push 20: top points to node with 20, next points to 10.

2. Step 2: Trace pop operation

   Pop removes top node (20), returns 20, top now points to node with 10.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   Last pushed, first popped = 20 [OK]

Hint: Stack pop returns last pushed value [OK]

Common Mistakes:

• Confusing order of push and pop
• Assuming pop returns bottom element
• Ignoring null check in pop

4. The following code attempts to implement a stack using an array but has a bug. What is the error?

class ArrayStack {
  int[] stack = new int[5];
  int top = -1;
  void push(int x) {
    top++;
    stack[top] = x;
  }
}

medium

A. stack array should be declared static

B. top should start at 0, not -1

C. Array size should be dynamic

D. No check for stack overflow before push

Solution

1. Step 1: Analyze push method

   Push increments top and assigns value without checking if top exceeds array size.

2. Step 2: Identify missing overflow check

   Without checking top < stack.length, pushing beyond capacity causes ArrayIndexOutOfBoundsException.

3. Final Answer:

   No check for stack overflow before push -> Option D

4. Quick Check:

   Missing overflow check = A [OK]

Hint: Always check stack size before pushing [OK]

Common Mistakes:

• Assuming top starts at 0 is mandatory
• Thinking array must be dynamic always
• Confusing static keyword necessity

5. You need to implement a stack for a program where the maximum number of elements is unknown and memory efficiency is important. Which implementation is best and why?

hard

A. Linked list stack, because it grows dynamically and uses memory only as needed.

B. Linked list stack, because it uses less memory overhead per element than arrays.

C. Array stack, because it provides faster push and pop operations always.

D. Array stack, because arrays use less memory per element and resizing is automatic.

Solution

1. Step 1: Consider unknown max size and memory efficiency

   Unknown max size means dynamic growth is needed; linked list grows as needed without fixed size.

2. Step 2: Compare memory usage and operation speed

   Linked list uses extra memory per node for pointers but avoids wasted space from large arrays; resizing arrays can be costly.

3. Step 3: Choose best fit

   Linked list stack fits unknown size and memory efficiency better despite pointer overhead.

4. Final Answer:

   Linked list stack, because it grows dynamically and uses memory only as needed. -> Option A

5. Quick Check:

   Dynamic size + memory efficient = D [OK]

Hint: Unknown size? Use linked list stack for dynamic memory [OK]

Common Mistakes:

• Assuming arrays resize automatically without cost
• Ignoring pointer memory overhead in linked lists
• Confusing speed with memory efficiency