力扣622.设计循环队列

• 

  • 通过数组索引构建一个虚拟的首尾相连的环
  • 当front = rear时 队列为空
  • 当front = rear + 1时 队列为满 (最后一位不存)

•   class MyCircularQueue {
        int front;
        int rear;
        int capacity;
        vector<int> elements;
    public:
        MyCircularQueue(int k) {
            //最后一位不存元素 多开一个
            capacity = k+1;
            elements = vector<int>(capacity);
            rear = front = 0;
        }
        
        bool enQueue(int value) {
            if(isFull())
                return false;
            elements[rear] = value;
            rear = (rear + 1) % capacity;
            return true;
        }
        
        bool deQueue() {
            if(isEmpty())
                return false;
            front = (front + 1) % capacity;
            return true;
        }
        
        int Front() {
            if(isEmpty())
                return -1;
            return elements[front];
        }
        
        int Rear() {
            if(isEmpty())
                return -1;
            return elements[(rear - 1 + capacity) % capacity];
        }
        
        bool isEmpty() {
            return rear == front;
        }
        
        bool isFull() {
            return ((rear + 1) % capacity) == front;
        }
    };