RingQueue

package ring_queue;

import java.util.HashSet;
import java.util.Set;

public class RingQueue<T> {

    private Node<T> head;
    private Node<T> tail;
    private int size;

    public void enqueue(T val, int id) {
        Node<T> node = new Node<T>(val, id);
        if(head == null) {
            head = node;
        } else {
            tail.next = node;
        }
        tail = node;
        tail.next = head;
        size++;
    }

    public int remove(Node<T> node) {
        int id = node.id;
        if(head == null) throw new IllegalStateException("head is null");
        if(head.id == id) {
            int toRemoveVal = (int) head.val;
            head = head.next;
            size--;
            return toRemoveVal;
        } else {
            Node<T> curr = head;
            while(true) {
                if(curr.next.id == id) {
                    int toRemoveVal = (int) curr.next.val;
                    curr.next = curr.next.next;
                    size--;
                    return toRemoveVal;
                }
                curr = curr.next;
            }
        }
    }

    public int size() {
        return size;
    }

    Set<Integer> seen = new HashSet<>();

    public void removeEvery(int k) {
        int position = 1;
        Node<T> curr = head;
        while(size > k) {
            if(position % k == 0) {
                if(!seen.contains(curr.id)) {
                    remove(curr);
                    System.out.println(this);
                }
            }
            position++;
            curr = curr.next;
        }
    }

    @Override
    public String toString() {
        StringBuilder result = new StringBuilder();
        int index = 0;
        Node<T> curr = head;
        while(true) {
            result.append(curr.val);
            if(index >= size) break; else result.append("->");
            index++;
            curr = curr.next;
        }

        return result.toString();
    }

    static class Node<T> {
        Node<T> next;
        final T val;
        final int id;

        public Node(T val, int id) {
            this.val = val;
            this.id = id;
        }

        public Node(T val, int id, Node<T> next) {
            this.next = next;
            this.val = val;
            this.id = id;
        }

        @Override
        public String toString() {
            return "Node{" +
                    "next=" + next +
                    ", id=" + id +
                    ", val=" + val +
                    '}';
        }
    }
}

package ring_queue;

public class Client {

    public static void main(String[] args) {
        RingQueue<Integer> queue = new RingQueue<>();
        for (int i = 0; i < 20; i++) {
            queue.enqueue(i, i);
        }

        System.out.println(queue);
        queue.removeEvery(5);
    }

}