Design Circular Queue

Description

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.

Solution(javascript)

/**
 * Initialize your data structure here. Set the size of the queue to be k.
 * @param {number} k
 */
const MyCircularQueue = function (k) {
  this.size = k
  this.queue = []
  this.start1 = 0
  this.end1 = 0
  this.start2 = 0
  this.end2 = 0
}

/**
 * Insert an element into the circular queue. Return true if the operation is successful.
 * @param {number} value
 * @return {boolean}
 */
MyCircularQueue.prototype.enQueue = function (value) {
  if (this.isFull()) {
    return false
  }
  if (this.end2 <= this.size - 1) {
    this.queue[this.end2++] = value
  } else {
    this.queue[this.end1++] = value
  }
  return true
}

/**
 * Delete an element from the circular queue. Return true if the operation is successful.
 * @return {boolean}
 */
MyCircularQueue.prototype.deQueue = function () {
  if (this.isEmpty()) {
    return false
  }
  if (this.queue[this.start2] !== undefined) {
    this.queue[this.start2++] = undefined
  } else {
    this.queue[this.start1++] = undefined
  }
  return true
}

/**
 * Get the front item from the queue.
 * @return {number}
 */
MyCircularQueue.prototype.Front = function () {
  if (this.isEmpty()) {
    return -1
  }
  return this.queue[this.start2] === undefined ? this.queue[this.start1] : this.queue[this.start2]
}

/**
 * Get the last item from the queue.
 * @return {number}
 */
MyCircularQueue.prototype.Rear = function () {
  if (this.isEmpty()) {
    return -1
  }
  return this.queue[this.end1 - 1] === undefined ? this.queue[this.end2 - 1] : this.queue[this.end1 - 1]
}

/**
 * Checks whether the circular queue is empty or not.
 * @return {boolean}
 */
MyCircularQueue.prototype.isEmpty = function () {
  if (this.end2 - this.start2 + this.end1 - this.start1 <= 0) {
    return true
  }
  return false
}

/**
 * Checks whether the circular queue is full or not.
 * @return {boolean}
 */
MyCircularQueue.prototype.isFull = function () {
  if (this.end2 - this.start2 + this.end1 - this.start1 >= this.size) {
    return true
  }
  return false
}