设计循环队列

• 在线：LeetCode: 622

题目

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.

代码实现

/**
 * Initialize your data structure here. Set the size of the queue to be k.
 * @param {number} k
 */
var MyCircularQueue = function (k) {
  this.q = new Array(k);
  this.head = -1;
  this.tail = -1;
  this.cap = k;
};

/**
 * 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() === true) {
    return false;
  }
  if (this.isEmpty() === true) {
    this.head = 0;
  }
  this.tail = (this.tail + 1) % this.cap;
  this.q[this.tail] = 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() === true) {
    return false;
  }
  if (this.head === this.tail) {
    this.head = -1;
    this.tail = -1;
    return true;
  }
  this.head = (this.head + 1) % this.cap;
  return true;
};

/**
 * Get the front item from the queue.
 * @return {number}
 */
MyCircularQueue.prototype.Front = function () {
  if (this.isEmpty() === true) {
    return -1;
  }
  return this.q[this.head];
};

/**
 * Get the last item from the queue.
 * @return {number}
 */
MyCircularQueue.prototype.Rear = function () {
  if (this.isEmpty() === true) {
    return -1;
  }
  return this.q[this.tail];
};

/**
 * Checks whether the circular queue is empty or not.
 * @return {boolean}
 */
MyCircularQueue.prototype.isEmpty = function () {
  return this.head === -1;
};

/**
 * Checks whether the circular queue is full or not.
 * @return {boolean}
 */
MyCircularQueue.prototype.isFull = function () {
  return (this.tail + 1) % this.cap === this.head;
};

/**
 * Your MyCircularQueue object will be instantiated and called as such:
 * var obj = new MyCircularQueue(k)
 * var param_1 = obj.enQueue(value)
 * var param_2 = obj.deQueue()
 * var param_3 = obj.Front()
 * var param_4 = obj.Rear()
 * var param_5 = obj.isEmpty()
 * var param_6 = obj.isFull()
 */

复杂度

• 时间复杂度：O(n)
• 空间复杂度：O(1)