LeetCode C++ 622. Design Circular Queue【设计/循环队列】中等-白红宇

LeetCode C++ 622. Design Circular Queue【设计/循环队列】中等

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发布时间：2019-04-28

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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 3circularQueue.enQueue(1);  // return truecircularQueue.enQueue(2);  // return truecircularQueue.enQueue(3);  // return truecircularQueue.enQueue(4);  // return false, the queue is fullcircularQueue.Rear();  // return 3circularQueue.isFull();  // return truecircularQueue.deQueue();  // return truecircularQueue.enQueue(4);  // return truecircularQueue.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.

题意：设计循环队列实现。循环队列是一种线性数据结构，其操作表现基于 FIFO（先进先出）原则并且队尾被连接在队首之后以形成一个循环。也被称为"环形缓冲器"。循环队列的一个好处是可以利用这个队列之前用过的空间。在一个普通队列里，一旦一个队列"满了"，就不能插入下一个元素，即使在队列前面仍有空间。但是使用循环队列，就能使用这些空间去存储新的值。

思路

感觉LeetCode上的设计题都可以替代平常的数据结构实现课程的学习了。代码如下：

class MyCircularQueue {
   private:    int *queue;    int capacity;    int size;    int front, rear; //[front, rear]public:    /** Initialize your data structure here. Set the size of the queue to be k. */    MyCircularQueue(int k) {
           queue = new int[capacity = k];        size = 0;        front = 0, rear = -1;    }        /** Insert an element into the circular queue. Return true if the operation is successful. */    bool enQueue(int value) {
           if (isFull()) return false;        ++size;        rear = (rear + 1) % capacity;        queue[rear] = value;        return true;    }        /** Delete an element from the circular queue. Return true if the operation is successful. */    bool deQueue() {
           if (isEmpty()) return false;        --size;        front = (front + 1) % capacity;        return true;    }        /** Get the front item from the queue. */    int Front() {
           if (isEmpty()) return -1;        return queue[front];    }        /** Get the last item from the queue. */    int Rear() {
           if (isEmpty()) return -1;        return queue[rear];    }        /** Checks whether the circular queue is empty or not. */    bool isEmpty() {
           return size == 0;    }        /** Checks whether the circular queue is full or not. */    bool isFull() {
           return size == capacity;    }};

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