Question

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.

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

Note:

• All values will be in the range of [0, 1000].
• The number of operations will be in the range of [1, 1000].
• Please do not use the built-in Queue library.

Difficulty:Medium

Category:

Analyze

Solution

class MyCircularQueue {
 public:
  /** Initialize your data structure here. Set the size of the queue to be k. */
  MyCircularQueue(int k) : buffer(k, -1), cnt(0), n(k), front(k - 1), rear(k - 1) {}

  /** Insert an element into the circular queue. Return true if the operation is successful. */
  bool enQueue(int value) {
    if (cnt == n) return false;
    buffer[rear--] = value;
    rear = (rear + n) % n;
    ++cnt;
    return true;
  }

  /** Delete an element from the circular queue. Return true if the operation is successful. */
  bool deQueue() {
    if (cnt == 0) return false;
    front = (front - 1) % n;
    --cnt;
    return true;
  }

  /** Get the front item from the queue. */
  int Front() { return cnt == 0 ? -1 : buffer[front]; }

  /** Get the last item from the queue. */
  int Rear() { return cnt == 0 ? -1 : buffer[(rear + 1) % n]; }

  /** Checks whether the circular queue is empty or not. */
  bool isEmpty() { return cnt == 0; }

  /** Checks whether the circular queue is full or not. */
  bool isFull() { return cnt == n; }

 private:
  vector<int> buffer;
  int cnt;
  int n;
  int front;
  int rear;
};