循环双端队列
设计一个循环双端队列，可以从头尾插入并删除
解题代码
思路：设置头尾指针，进行位置获取，添加和删除元素，设置一个记录队列元素大小的值。用于判满判空
var MyCircularDeque = function(k) {
this.queue = new Array(k); // 设置k个连续存储区
this.head = 0; // 头指针
this.tail = 0; // 尾指针
this.cnt = 0; // 队列中元素数量
};
/**
* Adds an item at the front of Deque. Return true if the operation is successful.
* @param {number} value
* @return {boolean}
*/
MyCircularDeque.prototype.insertFront = function(value) { // 头部插入
if (this.isFull()) return false;
this.head -= 1; // 头指针会有元素，所以在头部插入应该先把头指针往前走一步然后插入。
if (this.head === -1) this.head = this.queue.length - 1;
this.queue[this.head] = value;
this.cnt += 1;
return true;
};
/**
* Adds an item at the rear of Deque. Return true if the operation is successful.
* @param {number} value
* @return {boolean}
*/
MyCircularDeque.prototype.insertLast = function(value) { // 尾部插入
if (this.isFull()) return false;
this.queue[this.tail] = value;
this.tail += 1;
if (this.tail === this.queue.length) this.tail = 0;
this.cnt += 1;
return true;
};
/**
* Deletes an item from the front of Deque. Return true if the operation is successful.
* @return {boolean}
*/
MyCircularDeque.prototype.deleteFront = function() {
if (this.isEmpty()) return false;
this.head = (this.head + 1) % this.queue.length; // 头指针往后走一步，预防超过长度处理
this.cnt -= 1;
return true;
};
/**
* Deletes an item from the rear of Deque. Return true if the operation is successful.
* @return {boolean}
*/
MyCircularDeque.prototype.deleteLast = function() {
if (this.isEmpty()) return false;
this.tail = (this.tail - 1 + this.queue.length) % this.queue.length; // 尾指针往前走一步，预防出现 -1 进行处理。
this.cnt -= 1;
return true;
};
/**
* Get the front item from the deque.
* @return {number}
*/
MyCircularDeque.prototype.getFront = function() {
if (this.isEmpty()) return -1;
return this.queue[this.head];
};
/**
* Get the last item from the deque.
* @return {number}
*/
MyCircularDeque.prototype.getRear = function() {
if (this.isEmpty()) return -1;
return this.queue[(this.tail - 1 + this.queue.length) % this.queue.length]; // 尾指针对应的是最后一位元素的下一位，所以要减一，并预防出现负数。
};
/**
* Checks whether the circular deque is empty or not.
* @return {boolean}
*/
MyCircularDeque.prototype.isEmpty = function() {
return this.cnt === 0;
};
/**
* Checks whether the circular deque is full or not.
* @return {boolean}
*/
MyCircularDeque.prototype.isFull = function() {
return this.cnt === this.queue.length;
};
/**
* Your MyCircularDeque object will be instantiated and called as such:
* var obj = new MyCircularDeque(k)
* var param_1 = obj.insertFront(value)
* var param_2 = obj.insertLast(value)
* var param_3 = obj.deleteFront()
* var param_4 = obj.deleteLast()
* var param_5 = obj.getFront()
* var param_6 = obj.getRear()
* var param_7 = obj.isEmpty()
* var param_8 = obj.isFull()
*/
