1.3 - Queue.md

Queue

class Queue {
    class QueueNode {
        int val;
        QueueNode next;

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

    QueueNode first, last;

    void add(int val) {
        QueueNode node = new QueueNode(val);

        if (last != null) last.next = node;
        last = node;

        if (first == null) first = last;
    }

    int remove() {
        if (first == null) throw new EmptyQueueException();

        int val = first.val;
        first = first.next;
        if (first == null) last = null;

        return val;
    }

    int peek() {
        if (first == null) throw new EmptyQueueException();
        return first.val;
    }

    boolean isEmpty() {
        return first == null;
    }
}