LeetCode-in-Java

622. Design Circular Queue

Medium

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.

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

Constraints:

• 1 <= k <= 1000
• 0 <= value <= 1000
• At most 3000 calls will be made to enQueue, deQueue, Front, Rear, isEmpty, and isFull.

Solution

public class MyCircularQueue {
    private final DoubleLinkedNode dumyHead = new DoubleLinkedNode(0);
    private final int maxSize;
    private int size = 0;

    public MyCircularQueue(int k) {
        this.maxSize = k;
        dumyHead.left = dumyHead;
        dumyHead.right = dumyHead;
    }

    public boolean enQueue(int value) {
        if (size == maxSize) {
            return false;
        }
        DoubleLinkedNode node = new DoubleLinkedNode(value);
        DoubleLinkedNode right = dumyHead.right;
        dumyHead.right = node;
        node.left = dumyHead;
        node.right = right;
        right.left = node;
        size++;
        return true;
    }

    public boolean deQueue() {
        if (size == 0) {
            return false;
        }
        DoubleLinkedNode left = dumyHead.left;
        dumyHead.left = left.left;
        dumyHead.left.right = dumyHead;
        size--;
        return true;
    }

    public int rear() {
        if (size == 0) {
            return -1;
        }
        return dumyHead.right.val;
    }

    public int front() {
        if (size == 0) {
            return -1;
        }
        return dumyHead.left.val;
    }

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

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

    static class DoubleLinkedNode {
        private final int val;
        private DoubleLinkedNode left;
        private DoubleLinkedNode right;

        public DoubleLinkedNode(int val) {
            this.val = val;
        }
    }
}

/*
 * 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();
 */