[LeetCode] Problem 622 - Design Circular Queue

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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

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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.

Code

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private int[] queue;
private int front;
private int rear;
private int size;

public MyCircularQueue(int k) {
    queue = new int[k];
    front = 0;
    rear = -1;
    size = 0;
}

public boolean enQueue(int value) {
    if (!isFull()) {
        rear = (++rear) % queue.length;
        queue[rear] = value;
        size++;
        return true;
    }

    return false;
}

public boolean deQueue() {
    if (!isEmpty()) {
        front = (++front) % queue.length;
        size--;
        return true;
    }

    return false;
}

public int Front() {
    if (isEmpty())
        return -1;

    return queue[front];
}

public int Rear() {
    if (isEmpty())
        return -1;

    return queue[rear];
}

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

public boolean isFull() {
    return size == queue.length;
}