Peek Top Element of Stack in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to peek the top element of the stack.

DSA Python

def peek(stack):
    if not stack:
        return None
    return stack[1]

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

A[-1]

B[0]

Cpop()

Dappend()

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() removes the element instead of just peeking.

Using [0] accesses the bottom element, not the top.

To peek the top element of a stack implemented as a list, we access the last element using index [-1].

2fill in blank

medium

Complete the code to peek the top element safely, returning None if stack is empty.

DSA Python

def peek(stack):
    return stack[1] if stack else None

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

A[0]

Bpop()

Cappend()

D[-1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() removes the element.

Using [0] accesses the first element, not the top.

Using [-1] accesses the last element safely when stack is not empty; else None is returned.

3fill in blank

hard

Fix the error in the peek function to correctly return the top element without removing it.

DSA Python

def peek(stack):
    if len(stack) == 0:
        return None
    return stack[1]

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

A[-1]

Bpop()

C[len(stack)]

D[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() removes the element.

Using [len(stack)] causes IndexError.

Index [-1] returns the last element without removing it. pop() removes it, and [len(stack)] is out of range.

4fill in blank

hard

Fill both blanks to create a function that returns the top element or None if empty.

DSA Python

def peek(stack):
    if [1] == 0:
        return None
    return stack[2]

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

Alen(stack)

Bstack

C[-1]

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Checking stack instead of len(stack) for emptiness.

Using 0 index instead of -1 for top element.

Check if length of stack is zero to return None; else return last element with [-1].

5fill in blank

hard

Fill all three blanks to implement peek with exception handling for empty stack.

DSA Python

def peek(stack):
    try:
        return stack[1]
    except [2]:
        return [3]

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

A[-1]

BIndexError

CNone

D[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Catching wrong exception type.

Using [0] instead of [-1] to peek.

Access last element with [-1]; catch IndexError if stack is empty; return None then.