public class Queues {

    //queue from tail to head
    public static void main(String[] args) {

    }

    private class Node {
        int data;
        Node next;
        private Node(int data) {
            //node constructor
            this.data = data;
        }
    }

    private Node head;
    private Node tail;

    public void add(int elem) {
        //adds elem to queue (at tail)
        Node newNode = new Node(elem);
        if (tail == null) {
            tail = newNode;
            head = newNode;
        }
        else {
            newNode.next = tail;
            tail = newNode;
        }
        if (head == tail) head = newNode;
    }

    public int element() {
        //gets head of queue but doesn't remove it (similar to peek)
        return head.data;
    }

    public void offer(int elem) {
        //nice version of add
        add(elem); //nothing changes here because this is a linkedlist implementation
    }

    public int peek() {
        //returns head without deleting it
        return head.data;
    }

    public int poll() {
        //nice version of remove, returns null if elem doesn't exist (similar to pop)
        remove();
    }

    public int remove() {
        //removes element from head of queue and returns it (similar to pop)
        if (head == null) return -1;
        int temp = head.data;
        head = head.next;
        return temp;
    }

    public boolean isEmpty() {
        //returns true if queue is empty
        return (head == null);
    }

    public int size() {
        //returns size of queue
        int size = 0;
        Node current = tail;
        while (current != null) {
            size++;
            current = current.next;
        }
        return size;
    }

    public boolean find(int elem) {
        //returns true if elem exists in queue

        if (tail == null) return false;

        Node current = tail;
        while (current != null) {
            if (current.data == elem) return true;
            current = current.next;
        }
        return false;

    }




}