## 622. Design Circular Queue

Design 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.

Implementation the `MyCircularQueue` class:

• `MyCircularQueue(k)` Initializes the object with the size of the queue to be `k`.
• `int Front()` Gets the front item from the queue. If the queue is empty, return `-1`.
• `int Rear()` Gets the last item from the queue. If the queue is empty, return `-1`.
• `boolean enQueue(int value)` Inserts an element into the circular queue. Return `true` if the operation is successful.
• `boolean deQueue()` Deletes an element from the circular queue. Return `true` if the operation is successful.
• `boolean isEmpty()` Checks whether the circular queue is empty or not.
• `boolean isFull()` Checks whether the circular queue is full or not.

Example 1:

```Input
["MyCircularQueue", "enQueue", "enQueue", "enQueue", "enQueue", "Rear", "isFull", "deQueue", "enQueue", "Rear"]
[, , , , , [], [], [], , []]
Output
[null, true, true, true, false, 3, true, true, true, 4]

Explanation
MyCircularQueue myCircularQueue = new MyCircularQueue(3);
myCircularQueue.enQueue(1); // return True
myCircularQueue.enQueue(2); // return True
myCircularQueue.enQueue(3); // return True
myCircularQueue.enQueue(4); // return False
myCircularQueue.Rear();     // return 3
myCircularQueue.isFull();   // return True
myCircularQueue.deQueue();  // return True
myCircularQueue.enQueue(4); // return True
myCircularQueue.Rear();     // return 4
```

Constraints:

• `1 <= k <= 1000`
• `0 <= value <= 1000`
• At most `3000` calls will be made to `enQueue`, `deQueue``Front``Rear``isEmpty`, and `isFull`.

Follow up: Could you solve the problem without using the built-in queue?

## Rust Solution

``````struct MyCircularQueue {
k: usize,
start: usize,
end: usize,
data: Vec<i32>,
count: usize,
}

impl MyCircularQueue {
fn new(k: i32) -> Self {
let start = 0;
let end = 0;
let k = k as usize;
let data = vec![0; k];
let count = 0;
MyCircularQueue {
k,
start,
end,
data,
count,
}
}

fn en_queue(&mut self, value: i32) -> bool {
if self.count == self.k {
false
} else {
self.count += 1;
self.data[self.end] = value;
self.end = (self.end + 1) % self.k;
true
}
}

fn de_queue(&mut self) -> bool {
if self.count == 0 {
false
} else {
self.count -= 1;
self.start = (self.start + 1) % self.k;
true
}
}

fn front(&self) -> i32 {
if self.is_empty() {
-1
} else {
self.data[self.start]
}
}

fn rear(&self) -> i32 {
if self.is_empty() {
-1
} else {
self.data[(self.end + self.k - 1) % self.k]
}
}

fn is_empty(&self) -> bool {
self.count == 0
}

fn is_full(&self) -> bool {
self.count == self.k
}
}

#[test]
fn test() {
let mut queue = MyCircularQueue::new(3);
assert_eq!(queue.en_queue(1), true);
assert_eq!(queue.en_queue(2), true);
assert_eq!(queue.en_queue(3), true);
assert_eq!(queue.en_queue(4), false);
assert_eq!(queue.rear(), 3);
assert_eq!(queue.is_full(), true);
assert_eq!(queue.de_queue(), true);
assert_eq!(queue.en_queue(4), true);
assert_eq!(queue.rear(), 4);
}
``````

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