DesignCircularDeque.md

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---
Time：2019/4/15
Title: Design Circular Deque
Difficulty: Medium
Author: 小鹿
---

题目：Design Circular Deque

Design your implementation of the circular double-ended queue (deque).

Your implementation should support following operations:

• MyCircularDeque(k): Constructor, set the size of the deque to be k.
• insertFront(): Adds an item at the front of Deque. Return true if the operation is successful.
• insertLast(): Adds an item at the rear of Deque. Return true if the operation is successful.
• deleteFront(): Deletes an item from the front of Deque. Return true if the operation is successful.
• deleteLast(): Deletes an item from the rear of Deque. Return true if the operation is successful.
• getFront(): Gets the front item from the Deque. If the deque is empty, return -1.
• getRear(): Gets the last item from Deque. If the deque is empty, return -1.
• isEmpty(): Checks whether Deque is empty or not.
• isFull(): Checks whether Deque is full or not.

设计实现双端队列。 你的实现需要支持以下操作：

• MyCircularDeque(k)：构造函数,双端队列的大小为k。
• insertFront()：将一个元素添加到双端队列头部。 如果操作成功返回 true。
• insertLast()：将一个元素添加到双端队列尾部。如果操作成功返回 true。
• deleteFront()：从双端队列头部删除一个元素。 如果操作成功返回 true。
• deleteLast()：从双端队列尾部删除一个元素。如果操作成功返回 true。
• getFront()：从双端队列头部获得一个元素。如果双端队列为空，返回 -1。
• getRear()：获得双端队列的最后一个元素。 如果双端队列为空，返回 -1。
• isEmpty()：检查双端队列是否为空。
• isFull()：检查双端队列是否满了。

Example:

MyCircularDeque circularDeque = new MycircularDeque(3); // set the size to be 3
circularDeque.insertLast(1);			// return true
circularDeque.insertLast(2);			// return true
circularDeque.insertFront(3);			// return true
circularDeque.insertFront(4);			// return false, the queue is full
circularDeque.getRear();  			// return 2
circularDeque.isFull();				// return true
circularDeque.deleteLast();			// return true
circularDeque.insertFront(4);			// return true
circularDeque.getFront();			// 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 Deque library.

Solve:

▉ 算法思路

借助 Javascript 中数组中的 API 可快速实现一个双向队列。如：

• arr.pop() : 删除数组尾部最后一个数据。
• arr.push() ：在数组尾部插入一个数据。
• arr.shift()：数组头部删除第一个数据。
• arr.unshift()：数组头部插入一个数据。

以上数组提供的 API 使得更方便的对数组进行操作和模拟其他数据结构的操作，栈、队列等。

▉ 代码实现

 //双端列表构造
        var MyCircularDeque = function(k) {
            this.deque = [];
            this.size = k;
        };

        /**
        * Adds an item at the front of Deque. Return true if the operation is successful. 
        * @param {number} value
        * @return {boolean}
        * 功能:队列头部入队
        */
        MyCircularDeque.prototype.insertFront = function(value) {
            if(this.deque.length === this.size){
                return false;
            }else{
                this.deque.unshift(value);
                return true;
            }
        };

        /**
        * Adds an item at the rear of Deque. Return true if the operation is successful. 
        * @param {number} value
        * @return {boolean}
        * 功能：队列尾部入队
        */
        MyCircularDeque.prototype.insertLast = function(value) {
            if(this.deque.length === this.size){
                return false;
            }else{
                this.deque.push(value);
                return true;
            }
        };

        /**
        * Deletes an item from the front of Deque. Return true if the operation is successful.
        * @return {boolean}
        * 功能：队列头部出队
        */
        MyCircularDeque.prototype.deleteFront = function() {
            if(this.deque.length === 0){
                return false;
            }else{
                this.deque.shift();
                return true;
            }
        };

        /**
        * Deletes an item from the rear of Deque. Return true if the operation is successful.
        * @return {boolean}
        * 功能：队列尾部出队
        */
        MyCircularDeque.prototype.deleteLast = function() {
            if(this.deque.length === 0){
                return false;
            }else{
                this.deque.pop();
                return true;
            }
        };

        /**
        * Get the front item from the deque.
        * @return {number}
        * 功能：获取队列头部第一个数据
        */
        MyCircularDeque.prototype.getFront = function() {
            if(this.deque.length === 0){
                return -1;
            }else{
                return this.deque[0];
            }
        };

        /**
        * Get the last item from the deque.
        * @return {number}
        * 功能：获取队列尾部第一个数据
        */
        MyCircularDeque.prototype.getRear = function() {
            if(this.deque.length === 0){
                return -1;
            }else{
                return this.deque[this.deque.length - 1];
            }
        };

        /**
        * Checks whether the circular deque is empty or not.
        * @return {boolean}
        * 功能：判断双端队列是否为空
        */
        MyCircularDeque.prototype.isEmpty = function() {
            if(this.deque.length === 0){
                return true;
            }else{
                return false;
            }
        };

        /**
        * Checks whether the circular deque is full or not.
        * @return {boolean}
        * 功能：判断双端队列是否为满
        */
        MyCircularDeque.prototype.isFull = function() {
            if(this.deque.length === this.size){
                return true;
            }else{
                return false;
            }
        };

        //测试
        var obj = new MyCircularDeque(3)
        var param_1 = obj.insertFront(1)
        var param_2 = obj.insertLast(2)
        console.log('-----------------------------插入数据------------------------')
        console.log(`${param_1}${param_2}`)
        var param_3 = obj.deleteFront()
        var param_4 = obj.deleteLast()
        console.log('-----------------------------删除数据------------------------')
        console.log(`${param_3}${param_4}`)
        var param_5 = obj.getFront()
        var param_6 = obj.getRear()
        console.log('-----------------------------获取数据------------------------')
        console.log(`${param_5}${param_6}`)
        var param_7 = obj.isEmpty()
        var param_8 = obj.isFull()
        console.log('-----------------------------判断空/满------------------------')
        console.log(`${param_7}${param_8}`)