## # 622. Design Circular Queue

CDesign your implementation of the circular queue. The circular queue is a linear data structure in which the operations are performed based on FIFO (First In First Out) principle and the last position is connected back to the first position to make a circle. It is also called "Ring Buffer".

One of the benefits of the circular queue is that we can make use of the spaces in front of the queue. In a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. But using the circular queue, we can use the space to store new values.

Your implementation should support following operations:

MyCircularQueue(k): Constructor, set the size of the queue to be k.
Front: Get the front item from the queue. If the queue is empty, return -1.
Rear: Get the last item from the queue. If the queue is empty, return -1.
enQueue(value): Insert an element into the circular queue. Return true if the operation is successful.
deQueue(): Delete an element from the circular queue. Return true if the operation is successful.
isEmpty(): Checks whether the circular queue is empty or not.
isFull(): Checks whether the circular queue is full or not.

Example:

``````MyCircularQueue circularQueue = new MyCircularQueue(3); // set the size to be 3
circularQueue.enQueue(1);  // return true
circularQueue.enQueue(2);  // return true
circularQueue.enQueue(3);  // return true
circularQueue.enQueue(4);  // return false, the queue is full
circularQueue.Rear();  // return 3
circularQueue.isFull();  // return true
circularQueue.deQueue();  // return true
circularQueue.enQueue(4);  // return true
circularQueue.Rear();  // return 4
``````

### # Solution

Approach 1: use two pointers to maintain the front and end positions. Can also use a front pointer, then a length variable.

### # Code (Python)

Approach 1:

``````class MyCircularQueue:

def __init__(self, k: int):
"""
Initialize your data structure here. Set the size of the queue to be k.
"""
# idea: use start and end pointers, or a start and length pointer
self._queue = [None] * k # assume all inserted items != None
self._start = 0 # the index of the first item
self._end = 0 # the index of the last item + 1

def enQueue(self, value: int) -> bool:
"""
Insert an element into the circular queue. Return true if the operation is successful.
"""
if self.isFull():
return False
self._queue[self._end] = value
self._end = (self._end + 1) % len(self._queue)
return True

def deQueue(self) -> bool:
"""
Delete an element from the circular queue. Return true if the operation is successful.
"""
if self.isEmpty():
return False
self._queue[self._start] = None
self._start = (self._start + 1) % len(self._queue)
return True

def Front(self) -> int:
"""
Get the front item from the queue.
"""
if self.isEmpty():
return -1
return self._queue[self._start]

def Rear(self) -> int:
"""
Get the last item from the queue.
"""
if self.isEmpty():
return -1
return self._queue[self._end - 1]

def isEmpty(self) -> bool:
"""
Checks whether the circular queue is empty or not.
"""
return self._start == self._end and self._queue[self._start] == None

def isFull(self) -> bool:
"""
Checks whether the circular queue is full or not.
"""
return self._start == self._end and self._queue[self._start] != None
``````

Approach 1:

Approach 2: