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"]
[[3], [1], [2], [3], [4], [], [], [], [4], []]
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, deQueueFrontRearisEmpty, 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);
}

Having problems with this solution? Click here to submit an issue on github.