Basic enqueue/dequeue
Input
simulate([('enq', 1), ('enq', 2), ('deq', None)], 3)
Output
[True, True, 1]
Two enqueues succeed, dequeue returns the first enqueued value 1.
Full lesson preview
Implement a circular queue
Create a fixed-size circular queue class supporting enqueue, dequeue and access operations.
Python practice15 minStacks & QueuesIntermediateLast updated March 27, 2026
Problem statement
Implement a CircularQueue with a fixed capacity k. Provide operations: enqueue(value) -> bool (True if enqueued, False if full), dequeue() -> value or None (returns removed element or None if empty), front() -> value or None, rear() -> value or None, is_empty() -> bool, is_full() -> bool. Also provide a helper simulate(ops, k) that runs a sequence of operations and returns a list of results corresponding to each operation. Each operation in ops is a tuple: (op_name, value) where value is ignored for non-enqueue ops.
Task
Design and implement a circular buffer with constant-time enqueue/dequeue and index wrap-around.
Examples
Input format
A list of operation tuples and an integer capacity k.
Output format
A list of results (booleans for enqueue, values for dequeue/front/rear, booleans for is_empty/is_full).
Constraints
Capacity k is an integer between 1 and 10^4. Number of operations is between 1 and 10^4.
Samples
Sample 1
Input
simulate([('enq',1), ('enq',2), ('enq',3), ('enq',4)], 3)
Output
[True, True, True, False]
Third enqueue fills the queue, fourth fails.