622. Design Circular Queue

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.

Implementation the MyCircularQueue class:

• MyCircularQueue(k) Initializes the object with the size of the queue to be k.
• int Front() Gets the front item from the queue. If the queue is empty, return -1.
• int Rear() Gets the last item from the queue. If the queue is empty, return -1.
• boolean enQueue(int value) Inserts an element into the circular queue. Return true if the operation is successful.
• boolean deQueue() Deletes an element from the circular queue. Return true if the operation is successful.
• boolean isEmpty() Checks whether the circular queue is empty or not.
• boolean isFull() Checks whether the circular queue is full or not.

You must solve the problem without using the built-in queue data structure in your programming language.

class MyCircularQueue {
    deque<int> dq;
    int k;
public:
    MyCircularQueue(int k): k(k) {}
    
    bool enQueue(int value) {
        if(isFull()) return false;
        dq.push_back(value);
        return true;
    }
    
    bool deQueue() {
        if(isEmpty()) return false;
        dq.pop_front();
        return true;
    }
    
    int Front() {
        return isEmpty() ? -1 : dq.front();
    }
    
    int Rear() {
        return isEmpty() ? -1 : dq.back();
    }
    
    bool isEmpty() {
        return dq.empty();
    }
    
    bool isFull() {
        return dq.size() == k;
    }
};

/**
 * Your MyCircularQueue object will be instantiated and called as such:
 * MyCircularQueue* obj = new MyCircularQueue(k);
 * bool param_1 = obj->enQueue(value);
 * bool param_2 = obj->deQueue();
 * int param_3 = obj->Front();
 * int param_4 = obj->Rear();
 * bool param_5 = obj->isEmpty();
 * bool param_6 = obj->isFull();
 */

class MyCircularQueue {
    vector<int> q;
    int head = 0, tail = 0;
public:
    MyCircularQueue(int k) {
        q = vector<int>(k + 1);
    }
    
    bool enQueue(int value) {
        if(isFull()) return false;
        q[tail++] = value;
        tail %= q.size();
        return true;
    }
    
    bool deQueue() {
        if(isEmpty()) return false;
        head = (head + 1) % q.size();
        return true;
    }
    
    int Front() {
        if(isEmpty()) return -1;
        return q[head];
    }
    
    int Rear() {
        if(isEmpty()) return -1;
        return q[(tail - 1 + q.size()) % q.size()];
    }
    
    bool isEmpty() {
        return head == tail;
    }
    
    bool isFull() {
        return (tail + 1) % (q.size()) == head;
    }
};

/**
 * Your MyCircularQueue object will be instantiated and called as such:
 * MyCircularQueue* obj = new MyCircularQueue(k);
 * bool param_1 = obj->enQueue(value);
 * bool param_2 = obj->deQueue();
 * int param_3 = obj->Front();
 * int param_4 = obj->Rear();
 * bool param_5 = obj->isEmpty();
 * bool param_6 = obj->isFull();
 */