Stack Implementation Using Linked List in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the node structure for the linked list stack.

DSA Go

type Node struct {
	value int
	next *[1]
}

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

AStack

BList

CNode

DElement

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different struct name for the next pointer type.

Forgetting the pointer symbol * before the type.

The next field points to the next Node in the linked list.

2fill in blank

medium

Complete the code to initialize an empty stack with a top pointer.

DSA Go

type Stack struct {
	top *[1]
}

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

ANode

BElement

CStack

DList

Attempts:

3 left

💡 Hint

Common Mistakes

Using Stack type for top pointer instead of Node.

Missing the pointer symbol *.

The top points to the top Node in the stack.

3fill in blank

hard

Fix the error in the Push method to correctly add a new node on top of the stack.

DSA Go

func (s *Stack) Push(val int) {
	newNode := &Node{value: val}
	newNode.next = s.[1]
	s.top = newNode
}

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

Anext

Bhead

Cvalue

Dtop

Attempts:

3 left

💡 Hint

Common Mistakes

Using next instead of top for linking.

Not updating the top pointer after adding new node.

The new node's next should point to the current top node before updating top.

4fill in blank

hard

Fill both blanks to complete the Pop method that removes and returns the top value.

DSA Go

func (s *Stack) Pop() (int, bool) {
	if s.top == nil {
		return 0, false
	}
	val := s.top.value
	s.top = s.top.[1]
	return val, [2]
}

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

Anext

Btrue

Cfalse

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using prev instead of next for top pointer update.

Returning false instead of true on successful pop.

Pop moves the top pointer to the next node and returns true for success.

5fill in blank

hard

Fill all three blanks to complete the Peek method that returns the top value without removing it.

DSA Go

func (s *Stack) Peek() (int, bool) {
	if s.top == nil {
		return 0, [1]
	}
	return s.top.[2], [3]
}

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

Afalse

Bvalue

Ctrue

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Returning true when stack is empty.

Returning next pointer instead of value.

Peek returns false if empty, else returns the top value and true.

Practice

1. What is the main advantage of implementing a stack using a linked list instead of an array?

easy

A. Faster access to middle elements

B. Uses less memory for small stacks

C. Dynamic size, no fixed limit on number of elements

D. Allows random access to elements

Solution

1. Step 1: Understand stack size limitation in arrays

   Arrays have fixed size, so stack implemented with arrays has a fixed maximum capacity.

2. Step 2: Linked list allows dynamic memory allocation

   Linked list nodes are created as needed, so stack size can grow or shrink dynamically without fixed limit.

3. Final Answer:

   Dynamic size, no fixed limit on number of elements -> Option C

4. Quick Check:

   Linked list stack size is dynamic = B [OK]

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

Common Mistakes:

• Thinking linked list allows random access
• Confusing memory usage for small stacks
• Assuming linked list is always faster

2. Which of the following is the correct way to declare a node struct for a stack using linked list in Go?

easy

A. type Node struct { data int; next Node }

B. type Node struct { data int; next *Node }

C. type Node struct { data *int; next *Node }

D. type Node struct { data int; next interface{} }

Solution

1. Step 1: Understand pointer usage in linked list nodes

   Each node must point to the next node using a pointer type to avoid copying entire struct.

2. Step 2: Check each option for correct pointer declaration

   type Node struct { data int; next *Node } uses *Node pointer for next, which is correct. type Node struct { data int; next Node } uses Node (value), which causes copying. type Node struct { data *int; next *Node } uses *int for data which is unnecessary. type Node struct { data int; next interface{} } uses interface{} which is not type safe.

3. Final Answer:

   type Node struct { data int; next *Node } -> Option B

4. Quick Check:

   Next pointer must be *Node = A [OK]

Hint: Next node must be a pointer to Node struct [OK]

Common Mistakes:

• Using value type instead of pointer for next
• Using pointer for data unnecessarily
• Using interface{} instead of concrete type

3. What will be the output of the following Go code snippet implementing a stack push and pop?

package main
import "fmt"

type Node struct {
  data int
  next *Node
}

var top *Node = nil

func push(val int) {
  newNode := &Node{data: val, next: top}
  top = newNode
}

func pop() int {
  if top == nil {
    return -1
  }
  val := top.data
  top = top.next
  return val
}

func main() {
  push(10)
  push(20)
  push(30)
  fmt.Println(pop())
  fmt.Println(pop())
}

medium

A. 30
20

B. 10
20

C. 20
30

D. 10
30

Solution

1. Step 1: Trace push operations

   push(10) makes top point to node with 10; push(20) makes top point to node with 20 -> 10; push(30) makes top point to node with 30 -> 20 -> 10.

2. Step 2: Trace pop operations

   First pop returns 30 and moves top to 20 -> 10; second pop returns 20 and moves top to 10.

3. Final Answer:

   30 20 -> Option A

4. Quick Check:

   Stack LIFO order = 30 then 20 [OK]

Hint: Stack pops last pushed value first (LIFO) [OK]

Common Mistakes:

• Confusing push order with pop order
• Returning wrong node data on pop
• Not updating top pointer after pop

4. Identify the error in this pop function for a stack implemented using linked list in Go:

func pop() int {
  if top.next == nil {
    return -1
  }
  val := top.data
  top = top.next
  return val
}

medium

A. It does not check if top is nil before accessing top.next

B. It returns -1 incorrectly when stack is empty

C. It does not update top pointer after pop

D. It returns the wrong value from the stack

Solution

1. Step 1: Analyze nil checks in pop function

   The function checks if top.next == nil but does not check if top itself is nil, which can cause runtime panic if stack is empty.

2. Step 2: Understand correct empty stack check

   Correct check is if top == nil to detect empty stack before accessing top.next.

3. Final Answer:

   It does not check if top is nil before accessing top.next -> Option A

4. Quick Check:

   Check top == nil before top.next [OK]

Hint: Always check top == nil before accessing top.next [OK]

Common Mistakes:

• Checking top.next before top
• Returning wrong error value
• Forgetting to update top pointer

5. Given a stack implemented using a linked list, how would you implement a function to reverse the stack using only stack operations (push and pop) and no extra data structures?

hard

A. Traverse linked list and swap data values pairwise

B. Use a temporary array to store elements, then push back

C. Create a new stack and push elements popped from original stack

D. Use recursion: pop all elements, then push them back in reverse order

Solution

1. Step 1: Understand constraints of no extra data structures

   Using only push and pop means no arrays or new stacks allowed; recursion uses call stack implicitly.

2. Step 2: Use recursion to pop all elements and then push back in reverse

   Recursively pop elements until stack is empty, then insert elements at bottom recursively to reverse order.

3. Final Answer:

   Use recursion: pop all elements, then push them back in reverse order -> Option D

4. Quick Check:

   Recursion reverses stack without extra data structures [OK]

Hint: Recursion can reverse stack using call stack only [OK]

Common Mistakes:

• Using extra arrays or stacks violating constraints
• Trying to swap node data directly
• Not handling empty stack base case in recursion