Why Stack Exists and What Problems It Solves in DSA Go - See It Work

Why Stack Exists and What Problems It Solves

📖 Scenario: Imagine you are organizing a stack of plates in a kitchen. You can only add or remove the top plate. This is how a stack data structure works in computers.Stacks help solve problems where the last thing added is the first thing you want to remove, like undo actions in apps or checking if brackets in code match.

🎯 Goal: You will create a simple stack using a list in Go, add items to it, remove items, and see how the stack behaves.

📋 What You'll Learn

Create a slice called stack with initial elements

Create a variable called itemToAdd to add to the stack

Write code to add itemToAdd to the top of stack

Write code to remove the top item from stack

Print the final state of stack

💡 Why This Matters

🌍 Real World

Stacks are used in web browsers to keep track of pages visited, so you can go back to the previous page easily.

💼 Career

Understanding stacks is important for software developers to manage function calls, undo features, and expression evaluation.

1

Create the initial stack

Create a slice of strings called stack with these exact elements: "plate1", "plate2", "plate3"

DSA Go

// Create the initial stack slice
// Your code here

Hint

Use stack := []string{} to create a slice with the given elements.

2

Add an item to the stack

Create a string variable called itemToAdd and set it to "plate4"

DSA Go

package main

import "fmt"

func main() {
    stack := []string{"plate1", "plate2", "plate3"}
    
    // Create the variable itemToAdd with value "plate4"
    // Your code here
}

Hint

Use itemToAdd := "plate4" to create the variable.

3

Push the item onto the stack

Add itemToAdd to the end of the stack slice using append

DSA Go

package main

import "fmt"

func main() {
    stack := []string{"plate1", "plate2", "plate3"}
    itemToAdd := "plate4"
    
    // Add itemToAdd to stack
    // Your code here
}

Hint

Use stack = append(stack, itemToAdd) to add the item.

4

Pop the top item and print the stack

Remove the last item from stack by slicing it to exclude the last element, then print stack using fmt.Println(stack)

DSA Go

package main

import "fmt"

func main() {
    stack := []string{"plate1", "plate2", "plate3"}
    itemToAdd := "plate4"
    stack = append(stack, itemToAdd)
    
    // Remove the top item from stack
    // Print the stack
    // Your code here
}

Hint

Use stack = stack[:len(stack)-1] to remove the last item and fmt.Println(stack) to print.

Practice

1. Why do we use a stack data structure in programming?

easy

A. To sort numbers in ascending order automatically

B. To store data in random order for quick access

C. To keep track of function calls and return in the correct order

D. To store data permanently on disk

Solution

1. Step 1: Understand the role of stack in function calls

   Stacks help keep track of which function called which, so the program can return to the right place after finishing a function.

2. Step 2: Recognize the order of operations in stacks

   Stacks follow Last In First Out (LIFO), which matches how function calls return in reverse order.

3. Final Answer:

   To keep track of function calls and return in the correct order -> Option C

4. Quick Check:

   Stack = function call tracking [OK]

Hint: Stack tracks last function called first returned [OK]

Common Mistakes:

• Thinking stack stores data randomly
• Confusing stack with sorting
• Assuming stack stores data permanently

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

easy

A. stack = append(stack, element)

B. stack.push(element)

C. stack.add(element)

D. stack.insert(element)

Solution

1. Step 1: Recall how slices work in Go

   In Go, slices can be appended using the built-in append function.

2. Step 2: Identify the correct syntax for adding to stack

   Since stack is a slice, adding an element is done by stack = append(stack, element).

3. Final Answer:

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

4. Quick Check:

   Go slice append = push stack [OK]

Hint: Use append() to add element to slice stack [OK]

Common Mistakes:

• Using non-existent push method on slice
• Using add or insert which are not Go slice methods
• Forgetting to assign back to stack after append

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. 10

B. 30

C. Error

D. 20

Solution

1. Step 1: Trace the stack after each append

   After appending 10, 20, 30, stack = [10, 20, 30].

2. Step 2: Identify the last element and remove it

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

3. Final Answer:

   30 -> Option B

4. Quick Check:

   Last pushed = 30 popped = 30 [OK]

Hint: Last appended element is popped and printed [OK]

Common Mistakes:

• Printing first element instead of last
• Confusing slice indexing
• Expecting error due to slicing

4. Find the error in this Go code that tries to pop an element from a stack represented by a slice:

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

medium

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

B. Syntax error in slice operation

C. No error, code works fine

D. Stack slice is empty before pop

Solution

1. Step 1: Check indexing used to get last element

   stack[len(stack)] tries to access index equal to length, which is out of range (indexes go from 0 to len-1).

2. Step 2: Confirm correct index for last element

   The last element is at stack[len(stack)-1], so the code causes runtime error.

3. Final Answer:

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

4. Quick Check:

   Indexing error = Index out of range error when accessing stack[len(stack)] [OK]

Hint: Last element index is length-1, not length [OK]

Common Mistakes:

• Using len(stack) as index instead of len(stack)-1
• Assuming slice indexing starts at 1
• Ignoring runtime errors

5. You want to reverse a string using a stack in Go. Which approach correctly uses a stack to reverse the string "hello"?

hard

A. Sort characters alphabetically to reverse string

B. Append characters directly to a new string without stack

C. Use a queue to store characters and dequeue to reverse

D. Push each character onto a stack, then pop all to build reversed string

Solution

1. Step 1: Understand stack's LIFO property for reversing

   Pushing characters in order and popping reverses their order.

2. Step 2: Identify correct method to reverse string using stack

   Push all chars, then pop to build reversed string matches stack usage.

3. Final Answer:

   Push each character onto a stack, then pop all to build reversed string -> Option D

4. Quick Check:

   Stack LIFO reverses string [OK]

Hint: Stack reverses order by popping last pushed first [OK]

Common Mistakes:

• Using queue which reverses differently
• Appending without stack does not use stack concept
• Sorting changes order, not reverses