package datastructure;

import java.util.NoSuchElementException;
/**
 * Created by mkhwang on 2021/04/05
 * Email : orange2652@gmail.com
 * Github : http://github.com/myeongkwonhwang
 */
public class Queue<T> {

    private Node<T> first;
    private Node<T> last;

    public void add(T item){
        Node<T> t = new Node<>(item);
        if(last != null) last.next = t;
        last = t;
        if(first == null) first = last;
    }

    public T remove(){
        if(first == null)
            throw new NoSuchElementException();

        T data = first.data;
        first = first.next;

        if(first == null) last = null;

        return data;
    }

    public T peek() {
        if (first == null) throw new NoSuchElementException();

        return first.data;
    }

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

    class Node<T> {
        private T data;
        private Node<T> next;

        public Node(T data){
            this.data = data;
        }
    }
}

package datastructure;

import java.util.EmptyStackException;

/**
 * Created by mkhwang on 2021/04/05
 * Email : orange2652@gmail.com
 * Github : http://github.com/myeongkwonhwang
 */
public class Stack<T> {
    private Node<T> top;

    public T pop() {
        if(top == null){
            throw new EmptyStackException();
        }
        T item = top.data;
        top = top.next;
        return item;
    }

    public void push(T item){
        Node<T> t = new Node<>(item);
        t.next = top;
        top = t;
    }

    public T peek() {
        if (top == null){
            throw new EmptyStackException();
        }
        return top.data;
    }

    public boolean isEmpty(){
        return top == null;
    }

    class Node<T> {
        private T data;
        private Node<T> next;

        public Node(T data) {
            this.data = data;
        }
    }
}