Queue Using Two Stacks in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an element to the queue using stack push operation.

DSA Python

def enqueue(self, x):
    self.stack_in.[1](x)

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

Ainsert

Bpush

Cpop

Dappend

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of append causes removal instead of addition.

Using push is incorrect because Python lists do not have push method.

In Python, list's append method adds an element to the top of the stack.

2fill in blank

medium

Complete the code to check if the queue is empty by checking both stacks.

DSA Python

def is_empty(self):
    return len(self.stack_in) == 0 and len(self.stack_out) [1] 0

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A==

B!=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using != instead of == causes wrong empty check.

Using > or < does not correctly check for emptiness.

The queue is empty only if both stacks have zero length.

3fill in blank

hard

Fix the error in the dequeue method to correctly transfer elements from stack_in to stack_out.

DSA Python

def dequeue(self):
    if not self.stack_out:
        while self.stack_in:
            self.stack_out.[1](self.stack_in.pop())
    return self.stack_out.pop()

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

Aappend

Bpop

Cpush

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of append causes removal instead of addition.

Using push is invalid for Python lists.

We use append to add elements to stack_out after popping from stack_in.

4fill in blank

hard

Fill both blanks to complete the peek method that returns the front element without removing it.

DSA Python

def peek(self):
    if not self.stack_out:
        while self.stack_in:
            self.stack_out.[1](self.stack_in.pop())
    return self.stack_out[[2]]

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

Aappend

Bpop

C-1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of append causes errors.

Using index 0 returns the most recently added element, not the front.

We append elements from stack_in to stack_out, then return stack_out[-1] as the front of the queue.

5fill in blank

hard

Fill all three blanks to complete the full Queue class using two stacks.

DSA Python

class QueueUsingTwoStacks:
    def __init__(self):
        self.stack_in = []
        self.stack_out = []

    def enqueue(self, x):
        self.stack_in.[1](x)

    def dequeue(self):
        if not self.stack_out:
            while self.stack_in:
                self.stack_out.[2](self.stack_in.pop())
        return self.stack_out.pop()

    def is_empty(self):
        return len(self.stack_in) == 0 and len(self.stack_out) [3] 0

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

Aappend

Bpop

C==

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using push instead of append causes errors.

Using pop to add elements is incorrect.

Using != instead of == in is_empty causes wrong results.

The enqueue method uses append to add elements to stack_in. The dequeue method transfers elements using append to stack_out. The is_empty method checks if both stacks have zero length using ==.