Check if Stack is Empty or Full in DSA Go - Build from Scratch

Check if Stack is Empty or Full

📖 Scenario: You are building a simple stack to manage plates in a kitchen. The stack can hold only a limited number of plates. You want to check if the stack is empty (no plates) or full (maximum plates) before adding or removing plates.

🎯 Goal: Create a stack with a fixed size, add a configuration for maximum capacity, write functions to check if the stack is empty or full, and print the results.

📋 What You'll Learn

Create a stack as a slice of integers with exact values

Create a variable for maximum stack capacity

Write functions named isEmpty and isFull to check stack state

Print the results of isEmpty and isFull functions

💡 Why This Matters

🌍 Real World

Stacks are used in many real-world applications like undo features in text editors, managing function calls, and plate stacks in kitchens.

💼 Career

Understanding stack operations and state checks is fundamental for software developers working with data structures and algorithms.

1

Create the initial stack

Create a variable called stack as a slice of integers with these exact values: 10, 20, 30.

DSA Go

# Create a variable called stack as a slice of integers with values 10, 20, 30
# Your code here

Hint

Use stack := []int{10, 20, 30} to create the stack slice.

2

Add maximum capacity configuration

Add a variable called maxCapacity and set it to 5 to represent the maximum number of plates the stack can hold.

DSA Go

package main

func main() {
    stack := []int{10, 20, 30}
    // Add maxCapacity variable below
    // Your code here
}

Hint

Use maxCapacity := 5 to set the maximum capacity.

3

Write functions to check if stack is empty or full

Write two functions inside main: isEmpty that returns true if len(stack) == 0, and isFull that returns true if len(stack) == maxCapacity.

DSA Go

package main

func main() {
    stack := []int{10, 20, 30}
    maxCapacity := 5

    // Write isEmpty function below
    // Your code here

    // Write isFull function below
    // Your code here
}

Hint

Define isEmpty and isFull as functions returning boolean values based on the length of stack.

4

Print if the stack is empty or full

Use fmt.Println to print the results of calling isEmpty() and isFull() functions.

DSA Go

package main

import "fmt"

func main() {
    stack := []int{10, 20, 30}
    maxCapacity := 5

    isEmpty := func() bool {
        return len(stack) == 0
    }

    isFull := func() bool {
        return len(stack) == maxCapacity
    }

    // Print if stack is empty
    // Your code here

    // Print if stack is full
    // Your code here
}

Hint

Use fmt.Println("Is stack empty?", isEmpty()) and fmt.Println("Is stack full?", isFull()) to print the results.

Practice

1. What does the IsEmpty() function check in a stack data structure?

easy

A. If the stack has no elements inside

B. If the stack is full and cannot add more elements

C. If the stack has exactly one element

D. If the stack has more than one element

Solution

1. Step 1: Understand the purpose of IsEmpty()

   The IsEmpty() function checks whether the stack contains any elements or not.

2. Step 2: Identify what empty means for a stack

   An empty stack means it has zero elements inside, so no items to pop or peek.

3. Final Answer:

   If the stack has no elements inside -> Option A

4. Quick Check:

   IsEmpty() means stack is empty = true [OK]

Hint: Empty means zero elements inside stack [OK]

Common Mistakes:

• Confusing empty with full
• Thinking empty means one element
• Mixing IsEmpty with IsFull

2. Which of the following is the correct Go syntax to check if a stack is full when using a fixed size array?

easy

A. if len(stack) == 0 { /* stack is full */ }

B. if top > len(stack) { /* stack is full */ }

C. if top == len(stack) - 1 { /* stack is full */ }

D. if top == 0 { /* stack is full */ }

Solution

1. Step 1: Understand stack indexing in Go

   For a fixed size array stack, top points to the last filled index. The last valid index is length - 1.

2. Step 2: Check condition for full stack

   When top equals len(stack) - 1, the stack is full because no more elements can be added.

3. Final Answer:

   if top == len(stack) - 1 { /* stack is full */ } -> Option C

4. Quick Check:

   top == max index means full [OK]

Hint: Full means top equals last index (length - 1) [OK]

Common Mistakes:

• Using > instead of == for full check
• Checking if top == 0 for full
• Confusing length with top index

3. Given the following Go code, what will be printed?

type Stack struct {
    items []int
    top   int
}

func (s *Stack) IsEmpty() bool {
    return s.top == -1
}

func main() {
    s := Stack{items: make([]int, 5), top: -1}
    fmt.Println(s.IsEmpty())
    s.top = 4
    fmt.Println(s.IsEmpty())
}

medium

A. true\nfalse

B. false\ntrue

C. false\nfalse

D. true\ntrue

Solution

1. Step 1: Check initial top value and IsEmpty() result

   Initially, top is -1, so IsEmpty() returns true because stack is empty.

2. Step 2: Update top to 4 and check IsEmpty() again

   After setting top to 4, IsEmpty() returns false because stack now has elements.

3. Final Answer:

   true\nfalse -> Option A

4. Quick Check:

   top -1 means empty true, top 4 means not empty false [OK]

Hint: top -1 means empty, any other top means not empty [OK]

Common Mistakes:

• Assuming top 4 means empty
• Confusing slice length with top
• Ignoring initial top value

4. Find the error in this Go code snippet that checks if a stack is full:

func (s *Stack) IsFull() bool {
    return s.top == len(s.items)
}

medium

A. The function should return 's.top > len(s.items)' instead

B. The condition should be 's.top == len(s.items) - 1' to check full correctly

C. The function should check if 's.top == 0' to be full

D. No error, the code is correct

Solution

1. Step 1: Understand stack indexing for full condition

   Stack top index starts at -1 and max valid index is length - 1.

2. Step 2: Identify correct full condition

   Full means top equals last valid index, which is len(s.items) - 1, not len(s.items).

3. Final Answer:

   The condition should be 's.top == len(s.items) - 1' to check full correctly -> Option B

4. Quick Check:

   Full means top == max index (length - 1) [OK]

Hint: Full means top equals last index, not length [OK]

Common Mistakes:

• Using length instead of length - 1
• Checking top == 0 for full
• Returning wrong boolean condition

5. You have a stack implemented with a fixed size array of length 3 and a top index starting at -1. After pushing two elements, you pop one element, then push two more elements. Which statement about the stack state is correct?

hard

A. The stack is empty and top index is -1

B. The stack is not full and top index is 1

C. The stack is full but top index is 3

D. The stack is full and top index is 2

Solution

1. Step 1: Track stack operations and top index changes

   Start: top = -1 (empty). Push two elements: top = 1. Pop one element: top = 0. Push two elements: top = 2 (max index for length 3).

2. Step 2: Determine if stack is full

   Since top = 2 and max index is 2 (length 3 - 1), stack is full.

3. Final Answer:

   The stack is full and top index is 2 -> Option D

4. Quick Check:

   Push/pop changes top; top 2 means full for size 3 [OK]

Hint: Track top index after each push/pop carefully [OK]

Common Mistakes:

• Assuming top can be 3 for full
• Forgetting pop decreases top
• Confusing empty with full states