Check if Stack is Empty or Full in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the stack is empty.

DSA Python

def is_empty(stack):
    return len(stack) == [1]

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

A0

B1

C-1

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 instead of 0 to check empty stack.

The stack is empty when its length is 0.

2fill in blank

medium

Complete the code to check if the stack is full given max size.

DSA Python

def is_full(stack, max_size):
    return len(stack) == [1]

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

Amax_size - 1

Bmax_size

Clen(stack)

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using max_size - 1 instead of max_size.

The stack is full when its length equals max_size.

3fill in blank

hard

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

DSA Python

def is_empty(stack):
    if stack == [1]:
        return True
    else:
        return False

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

AFalse

BNone

C0

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing stack to None instead of [].

An empty stack is represented by an empty list [].

4fill in blank

hard

Fill both blanks to check if stack is full given max size.

DSA Python

def is_full(stack, max_size):
    if len(stack) [1] max_size:
        return True
    else:
        return [2]

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

A==

BFalse

C!=

DTrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' in condition.

Returning True when stack is not full.

Stack is full if length equals max_size; otherwise, return False.

5fill in blank

hard

Fill all three blanks to check if stack is empty or full.

DSA Python

def check_stack(stack, max_size):
    if len(stack) [1] 0:
        return '[2]'
    elif len(stack) [3] max_size:
        return 'Full'
    else:
        return 'Not full or empty'

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

A==

BEmpty

C!=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' to check empty or full.

Check if length is 0 for empty, equals max_size for full.

Practice

1. What does the isEmpty() function check in a stack?

easy

A. If the stack has exactly one element

B. If the stack is full

C. If the stack has more than one element

D. If the stack has no elements

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, so isEmpty() returns true if no elements are present.

3. Final Answer:

   If the stack has no elements -> Option D

4. Quick Check:

   Empty stack means no elements = true [OK]

Hint: Empty stack means zero elements inside [OK]

Common Mistakes:

• Confusing empty with full
• Thinking it checks for one element
• Assuming it checks for capacity

2. Which of the following is the correct syntax to check if a stack named stack is full in Python assuming max size is stored in max_size and current size in top?

easy

A. if top == max_size: print('Stack is full')

B. if top > max_size: print('Stack is full')

C. if top < max_size: print('Stack is full')

D. if top != max_size: print('Stack is full')

Solution

1. Step 1: Understand stack full condition

   A stack is full when the current top index equals the maximum allowed size.

2. Step 2: Match condition with syntax

   The correct check is top == max_size to confirm fullness.

3. Final Answer:

   if top == max_size: print('Stack is full') -> Option A

4. Quick Check:

   Full stack when top equals max size [OK]

Hint: Full stack means top equals max size [OK]

Common Mistakes:

• Using greater than instead of equal
• Using less than for full check
• Using not equal instead of equal

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

class Stack:
    def __init__(self, max_size):
        self.stack = []
        self.max_size = max_size
    def isFull(self):
        return len(self.stack) == self.max_size
    def isEmpty(self):
        return len(self.stack) == 0

s = Stack(2)
s.stack.append(10)
s.stack.append(20)
print(s.isFull())
print(s.isEmpty())

medium

A. False\nTrue

B. True\nTrue

C. True\nFalse

D. False\nFalse

Solution

1. Step 1: Check stack contents after append

   Two elements (10, 20) are added, so length is 2 which equals max_size.

2. Step 2: Evaluate isFull and isEmpty

   isFull() returns True because length equals max_size; isEmpty() returns False because stack is not empty.

3. Final Answer:

   True False -> Option C

4. Quick Check:

   Stack full = True, empty = False [OK]

Hint: Full if length equals max size; empty if length zero [OK]

Common Mistakes:

• Confusing isFull and isEmpty return values
• Ignoring stack length after append
• Assuming stack is empty after append

4. Find the error in the following code that checks if a stack is empty:

class Stack:
    def __init__(self):
        self.stack = []
    def isEmpty(self):
        if self.stack == 0:
            return True
        else:
            return False

s = Stack()
print(s.isEmpty())

medium

A. Missing return statement in isEmpty

B. Comparing list to integer zero causes error

C. Stack initialization is incorrect

D. Print statement syntax is wrong

Solution

1. Step 1: Analyze the isEmpty condition

   The code compares self.stack == 0, but self.stack is a list, not a number.

2. Step 2: Identify correct way to check empty list

   To check if list is empty, use len(self.stack) == 0 or simply not self.stack.

3. Final Answer:

   Comparing list to integer zero causes error -> Option B

4. Quick Check:

   List cannot be compared to number 0 [OK]

Hint: Check list emptiness with length or not operator [OK]

Common Mistakes:

• Comparing list directly to 0
• Forgetting list length check
• Using wrong comparison operator

5. You have a stack with max size 3. After pushing 3 elements, you pop one element and then check if the stack is full or empty. What will be the correct output of isFull() and isEmpty() methods?

class Stack:
    def __init__(self, max_size):
        self.stack = []
        self.max_size = max_size
    def push(self, val):
        if len(self.stack) < self.max_size:
            self.stack.append(val)
    def pop(self):
        if not self.isEmpty():
            return self.stack.pop()
    def isFull(self):
        return len(self.stack) == self.max_size
    def isEmpty(self):
        return len(self.stack) == 0

s = Stack(3)
s.push(1)
s.push(2)
s.push(3)
s.pop()
print(s.isFull())
print(s.isEmpty())

hard

A. False\nFalse

B. True\nFalse

C. False\nTrue

D. True\nTrue

Solution

1. Step 1: Track stack size after operations

   Initially push 3 elements, stack size = 3 (full). After pop, size reduces to 2.

2. Step 2: Evaluate isFull and isEmpty

   Since size is 2 and max_size is 3, isFull() returns False. Stack is not empty, so isEmpty() returns False.

3. Final Answer:

   False False -> Option A

4. Quick Check:

   Stack size 2 < max size 3, not empty [OK]

Hint: Pop reduces size; full only if size equals max [OK]

Common Mistakes:

• Assuming stack is still full after pop
• Assuming stack is empty after pop
• Ignoring size changes after pop