Queue Using Stacks 20 XP Easy

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Implement a queue using only two stacks. This classic problem teaches how data structures can simulate each other.

q = MyQueue()
q.push(1)    # stack_in: [1]
q.push(2)    # stack_in: [1, 2]
q.peek()     # → 1 (front of queue)
q.pop()      # → 1 (FIFO)
q.empty()    # → False

The two-stack trick:

stack_in: Always push new elements here
stack_out: Pop from here for dequeue/peek
When stack_out is empty, dump all of stack_in into stack_out (reverses order!)
LIFO + LIFO = FIFO — reversing twice gives you queue order

Amortized O(1) per operation — each element is moved at most twice (once into stack_in, once into stack_out).

📋 Instructions

Implement MyQueue using two stacks. Test push, peek, pop, and empty operations.

push() always appends to stack_in. For pop/peek, if stack_out is empty, transfer ALL elements from stack_in to stack_out (pop from stack_in, push to stack_out). Then pop/peek from stack_out.

🧪 Test Cases

Input

q.peek()

Expected

1

Test case 1

Input

q.pop()

Expected

1

Test case 2

Input

q.empty()

Expected

False

Boolean check

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main.py

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Output

Ready. Press ▶ Run or Ctrl+Enter.

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