622. Design Circular Queue

Description

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.

Constraints

• 1 <= k <= 1000

• 0 <= value <= 1000

• At most 3000 calls will be made to enQueue, deQueue, Front, Rear, isEmpty, and isFull.

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

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

Solutions

Solution 1

/**
 * Time complexity : 
 * Space complexity : 
 */

class MyCircularQueue {
    
    private int[] data;
    private int head;
    private int tail;
    private int size;

    public MyCircularQueue(int k) {
        head = -1;
        tail = -1;
        data = new int[k];
        size = k;
    }
    
    public boolean enQueue(int value) {
        if(isFull()) {
            return false;
        }
        if(isEmpty()) {
            head = 0;
        }
        tail = (tail + 1) % size;
        data[tail] = value;
        return true;
    }
    
    public boolean deQueue() {
        if(isEmpty()) {
            return false;
        }
        if(head == tail) {
            head = -1;
            tail = -1;
            return true;
        }
        head = (head + 1) % size;
        return true;
    }
    
    public int Front() {
        if(isEmpty()) {
            return -1;
        }
        return data[head];
    }
    
    public int Rear() {
        if(isEmpty()) {
            return -1;
        }
        return data[tail];
    }
    
    public boolean isEmpty() {
        return head == -1;
    }
    
    public boolean isFull() {
        return ((tail + 1) % size) == head;
    }
}

/**
 * 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();
 */

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