LeetCode #622. Design Circular Queue

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本文介绍了一种遵循FIFO原则的环形队列数据结构设计，详细阐述了其构造方法、插入、删除、检查队列状态等操作，并通过实例展示了如何使用环形队列。环形队列能有效利用队头前的空间，提高内存利用率。

题目描述：

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.

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