23_Design_Circular_queue.java

// 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.

// Implement 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. 

 

// Example 1:

// Input
// ["MyCircularQueue", "enQueue", "enQueue", "enQueue", "enQueue", "Rear", "isFull", "deQueue", "enQueue", "Rear"]
// [[3], [1], [2], [3], [4], [], [], [], [4], []]
// Output
// [null, true, true, true, false, 3, true, true, true, 4]

// Explanation
// MyCircularQueue myCircularQueue = new MyCircularQueue(3);
// myCircularQueue.enQueue(1); // return True
// myCircularQueue.enQueue(2); // return True
// myCircularQueue.enQueue(3); // return True
// myCircularQueue.enQueue(4); // return False
// myCircularQueue.Rear();     // return 3
// myCircularQueue.isFull();   // return True
// myCircularQueue.deQueue();  // return True
// myCircularQueue.enQueue(4); // return True
// myCircularQueue.Rear();     // return 4











// Leetcode optimal solution same just logical operator

class MyCircularQueue {
    int[] arr;
    int front, rear, size, capacity;

    public MyCircularQueue(int k) {
        arr = new int[k];
        capacity = k;
        size = 0;
        front = 0;
        rear = 0;
    }

    public boolean enQueue(int value) {
        if (isFull()) return false;

        arr[rear] = value;
        rear = (rear + 1) % capacity;
        size++;
        return true;
    }

    public boolean deQueue() {
        if (isEmpty()) return false;

        front = (front + 1) % capacity;
        size--;
        return true;
    }

    public int Front() {
        return isEmpty() ? -1 : arr[front];
    }

    public int Rear() {
        return isEmpty() ? -1 : arr[(rear - 1 + capacity) % capacity];
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public boolean isFull() {
        return size == capacity;
    }
}


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










// Optimal solution

class MyCircularQueue {
    private int[] q;
    private int front;
    private int curr;
    private int maxcap;

    public MyCircularQueue(int k) {
        q=new int[k];
        front=0;
        curr=0;
        maxcap=k;
    }
    
    public boolean enQueue(int value) {
        if(isFull()) return false;
        int rear=(front+curr)%maxcap;
        q[rear]=value;
        curr++;
        return true;
    }
    
    public boolean deQueue() {
        if(isEmpty()) return false;
        front=(front+1)%maxcap;
        curr--;
        return true;
    }
    
    public int Front() {
        if(isEmpty()) return -1;
        return q[front];
    }
    
    public int Rear() {
        if(isEmpty()) return -1;
        int rear=(front+curr-1)%maxcap;
        return q[rear];
    }
    
    public boolean isEmpty() {
        return curr==0;
    }
    
    public boolean isFull() {
        return curr == maxcap; 
    }
}

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