Stack Concept and LIFO Principle in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto the stack.

DSA Go

stack = []
stack.[1](5)
print(stack)

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

Apop

Bremove

Cinsert

Dappend

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of append removes an element instead of adding.

Using remove tries to delete a specific value, not add.

The append method adds an element to the top of the stack.

2fill in blank

medium

Complete the code to remove the top element from the stack.

DSA Go

stack = [1, 2, 3]
top = stack.[1]()
print(top, stack)

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

Apop

Bappend

Cremove

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using append adds an element instead of removing.

Using remove needs a value, not an index.

The pop method removes and returns the last element, which is the top of the stack.

3fill in blank

hard

Fix the error in the code to correctly check if the stack is empty.

DSA Go

stack = []
if len(stack) [1] 0:
    print("Stack is empty")

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

A==

B>

C!=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' checks for not empty, opposite of what is needed.

Using '>' or '<' does not correctly check for empty.

To check if the stack is empty, length should be equal to zero.

4fill in blank

hard

Fill both blanks to create a stack and push an element.

DSA Go

stack = [1]
stack.[2](10)
print(stack)

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

A[]

Bappend

Cpop

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using {} creates a dictionary, not a list.

Using pop tries to remove instead of add.

The stack is an empty list []. Use append to add an element.

5fill in blank

hard

Fill all three blanks to pop the top element and print it.

DSA Go

stack = [5, 6, 7]
top = stack.[1]()
print("Top element:", [2])
print("Stack now:", [3])

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

Aappend

Btop

Cstack

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using append instead of pop changes the stack incorrectly.

Printing the wrong variable name causes errors.

Use pop to remove the top element, print the popped element stored in top, and then print the updated stack.

Practice

1. What does the LIFO principle mean in the context of a stack?

easy

A. Last In, First Out - the last element added is the first to be removed

B. Last In, First Out - the first element added is the first to be removed

C. First In, First Out - the first element added is the first to be removed

D. First In, Last Out - the first element added is the last to be removed

Solution

1. Step 1: Understand LIFO meaning

   LIFO stands for Last In, First Out, meaning the last item added to the stack is the first one removed.

2. Step 2: Match with stack behavior

   Stacks follow LIFO, so the last pushed element is popped first.

3. Final Answer:

   Last In, First Out - the last element added is the first to be removed -> Option A

4. Quick Check:

   LIFO = Last In, First Out [OK]

Hint: Remember stack removes newest item first [OK]

Common Mistakes:

• Confusing LIFO with FIFO
• Thinking first added is removed first
• Mixing up stack with queue behavior

2. Which of the following is the correct way to push an element '5' onto a stack named stack in Go?

easy

A. stack.push(5)

B. stack = append(stack, 5)

C. stack.add(5)

D. stack.insert(5)

Solution

1. Step 1: Recall Go slice push syntax

   In Go, stacks are often slices; to push, use append(slice, value).

2. Step 2: Check options for correct syntax

   Only stack = append(stack, 5) correctly adds 5 to the stack slice.

3. Final Answer:

   stack = append(stack, 5) -> Option B

4. Quick Check:

   Go stack push uses append [OK]

Hint: Use append to add elements to Go slices [OK]

Common Mistakes:

• Using non-existent push method on slice
• Using add or insert which are invalid for slices
• Forgetting to assign append result back

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

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

medium

A. 30

B. 20

C. 10

D. Error

Solution

1. Step 1: Trace stack push operations

   Elements 10, 20, 30 are pushed in order; stack is [10, 20, 30].

2. Step 2: Pop last element

   last = stack[len(stack)-1] gets 30; then stack is sliced to remove last element.

3. Final Answer:

   30 -> Option A

4. Quick Check:

   Last pushed element popped = 30 [OK]

Hint: Last appended element is popped first [OK]

Common Mistakes:

• Printing first element instead of last
• Forgetting to slice stack after pop
• Confusing index for pop operation

4. Identify the error in this Go code that tries to pop an element from a stack:

stack := []int{1, 2, 3}
last := stack[len(stack)]
stack = stack[:len(stack)-1]
fmt.Println(last)

medium

A. Cannot print variable last

B. Syntax error in slice operation

C. Index out of range error due to accessing stack[len(stack)]

D. No error, code runs correctly

Solution

1. Step 1: Check index used for popping

   Indexing with stack[len(stack)] is invalid because slice indices go from 0 to len(stack)-1.

2. Step 2: Identify error type

   This causes an index out of range runtime error.

3. Final Answer:

   Index out of range error due to accessing stack[len(stack)] -> Option C

4. Quick Check:

   Index must be len(stack)-1, not len(stack) [OK]

Hint: Use len(stack)-1 for last index [OK]

Common Mistakes:

• Using len(stack) as index
• Ignoring zero-based indexing
• Assuming code runs without error

5. Given a stack implemented as a slice in Go, how would you reverse the order of elements using only stack operations (push and pop)?

hard

A. Pop elements and discard them to reverse the stack

B. Push elements onto the same stack again without popping

C. Use a queue instead of a stack to reverse elements

D. Pop all elements into a temporary slice, then push them back in order

Solution

1. Step 1: Pop all elements from original stack

   Pop elements one by one and store them in a temporary slice to hold reversed order.

2. Step 2: Push elements back to original stack

   Push elements from temporary slice back to stack; this reverses the order due to LIFO.

3. Final Answer:

   Pop all elements into a temporary slice, then push them back in order -> Option D

4. Quick Check:

   Reversing stack needs pop then push back [OK]

Hint: Pop all, then push back reverses stack [OK]

Common Mistakes:

• Pushing without popping does not reverse
• Discarding elements loses data
• Using queue is not stack operation