Queue vs Stack When to Use Which in DSA Go - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an element to the end of a queue.

DSA Go

queue := []int{}
queue = append(queue, [1])

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

Aelement

B10

C5

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number instead of the variable name for the element.

Trying to add to the front of the queue instead of the end.

In Go, to add an element to the end of a slice (used as a queue), we use append with the element name. Here, element is the correct placeholder for the item to add.

2fill in blank

medium

Complete the code to remove the last element from a stack.

DSA Go

stack = stack[:len(stack) [1] 1]

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

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of subtraction.

Using multiplication or division which are incorrect here.

To remove the last element from a stack implemented as a slice, we slice up to len(stack)-1. The minus sign - is used to subtract 1.

3fill in blank

hard

Fix the error in the code to check if a queue is empty.

DSA Go

if len(queue) [1] 0 {
    fmt.Println("Queue is empty")
}

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

A!=

B==

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using != which checks for non-empty.

Using > or < which do not correctly check emptiness.

To check if a queue is empty, we compare its length to zero using ==. If length equals zero, the queue is empty.

4fill in blank

hard

Fill both blanks to implement pushing an element onto a stack and then popping it.

DSA Go

stack = append(stack, [1])
last := stack[len(stack) [2] 1]

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

Aelement

B+

C-

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '-' when accessing the last element.

Using 'item' instead of 'element' for pushing.

To push, append the element to the stack. To pop, access the last element using len(stack)-1.

5fill in blank

hard

Fill all three blanks to create a queue, enqueue an element, and dequeue it.

DSA Go

queue := []int{}
queue = append(queue, [1])
dequeued := queue[[2]]
queue = queue[[3]:]

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

Aelement

B0

C1

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong indices for dequeue.

Using 'item' instead of 'element' for enqueue.

We start with an empty queue. Enqueue by appending element. Dequeue by taking the first element at index 0 and then slicing the queue from index 1 onward.

Practice

1. Which data structure should you use when you need to process items in the exact order they arrive, like customers waiting in line?

easy

A. Queue, because it processes items in First-In-First-Out order

B. Stack, because it processes items in Last-In-First-Out order

C. Array, because it allows random access

D. Tree, because it organizes data hierarchically

Solution

1. Step 1: Understand the order requirement

   Processing items in the exact order they arrive means First-In-First-Out (FIFO).

2. Step 2: Match data structure to FIFO

   Queue follows FIFO, so it fits the requirement perfectly.

3. Final Answer:

   Queue, because it processes items in First-In-First-Out order -> Option A

4. Quick Check:

   FIFO = Queue [OK]

Hint: FIFO means use Queue, like a line at a store [OK]

Common Mistakes:

• Confusing FIFO with LIFO
• Choosing Stack for order-sensitive tasks
• Thinking arrays maintain insertion order automatically

2. Which of the following is the correct way to push an element onto a stack in Go using a slice named stack?

easy

A. stack = append(element, stack...)

B. stack = stack[:len(stack)-1]

C. stack = stack + element

D. stack = append(stack, element)

Solution

1. Step 1: Recall how to add elements to a slice

   In Go, append(slice, value) adds value to the end of slice.

2. Step 2: Identify correct push operation

   Pushing onto a stack means adding to the top, which is the end of the slice, so stack = append(stack, element) is correct.

3. Final Answer:

   stack = append(stack, element) -> Option D

4. Quick Check:

   Push = append to slice end [OK]

Hint: Use append to add on top of stack slice [OK]

Common Mistakes:

• Using slicing to add elements instead of append
• Trying to add element at the front incorrectly
• Using + operator which is invalid for slices

3. What will be the output of the following Go code snippet?

queue := []int{1, 2, 3}
// Dequeue operation
queue = queue[1:]
fmt.Println(queue)

medium

A. [2 3]

B. []

C. [3]

D. [1 2 3]

Solution

1. Step 1: Understand the dequeue operation

   Dequeue removes the first element, so slicing from index 1 removes the first element.

2. Step 2: Apply slicing to queue

   Original queue is [1 2 3], after queue = queue[1:], queue becomes [2 3].

3. Final Answer:

   [2 3] -> Option A

4. Quick Check:

   queue[1:] removes first element [OK]

Hint: queue = queue[1:] removes front element [OK]

Common Mistakes:

• Thinking queue[1:] removes last element
• Confusing slice syntax with pop operation
• Expecting original queue unchanged

4. The following Go code intends to pop an element from a stack implemented as a slice. What is the error?

stack := []int{10, 20, 30}
popped := stack[len(stack)]
stack = stack[:len(stack)-1]
fmt.Println(popped, stack)

medium

A. Syntax error due to missing parentheses

B. Index out of range error when accessing stack[len(stack)]

C. Popped element is always zero

D. Stack slice is not updated correctly

Solution

1. Step 1: Check index used for popping

   Indexing in Go slices is zero-based, so last element is at len(stack)-1, not len(stack).

2. Step 2: Identify error cause

   Accessing stack[len(stack)] causes index out of range error because it is beyond last index.

3. Final Answer:

   Index out of range error when accessing stack[len(stack)] -> Option B

4. Quick Check:

   Last index = len(stack)-1, not len(stack) [OK]

Hint: Last element index is len(slice)-1, not len(slice) [OK]

Common Mistakes:

• Using len(slice) as index instead of len(slice)-1
• Not updating slice after pop
• Confusing pop with dequeue operation

5. You need to design a system that tracks the most recent 5 user actions to allow undo functionality. Which data structure is best and why?

hard

A. Array, because it allows random access to any action

B. Queue, because it keeps actions in order and removes oldest first

C. Stack, because it allows undo by removing the most recent action first

D. Linked list, because it allows fast insertion anywhere

Solution

1. Step 1: Understand undo functionality

   Undo removes the most recent action first, which is Last-In-First-Out (LIFO) behavior.

2. Step 2: Match data structure to LIFO

   Stack follows LIFO, so it is best to track recent actions and undo them in reverse order.

3. Final Answer:

   Stack, because it allows undo by removing the most recent action first -> Option C

4. Quick Check:

   Undo = LIFO = Stack [OK]

Hint: Undo needs LIFO, so use Stack [OK]

Common Mistakes:

• Choosing Queue which removes oldest first
• Thinking array random access helps undo
• Ignoring order of undo operations