[자료구조/Java] Queue 구현하기 in Java

 

www.youtube.com/watch?v=W3jNbNGyjMs

 

선입선출 방식(First-In First-Out, FIFO)

 

1) add()

2) remove()

3) peek()

4) isEmpty()

 

import java.util.NoSuchElementException;

class Queue<T>{
	class Node<T>{
    	private T data;
        private Node<T> next;
        
        public Node(T data){
        	this.data = data;
        }
    }
    
    private Node<T> first;
    private Node<T> last;
    
    public void add(T item){
    	Node<T> t = new Node<T>(item);
        
        if(last != null){
        	last.next = t;
        }
        last = t;
        //큐가 비어있을 때
        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;
    }
}

public class Main{
	public static void main(String[] args){
    	Queue<Integer> queue = new Queue<Integer>();
        q.add(1);
        q.add(2);
        q.add(3);
        q.add(4);
        System.out.println(q.remove());
        System.out.println(q.remove());
        System.out.println(q.peek());
        System.out.println(q.remove());
        System.out.println(q.isEmpty());
        System.out.println(q.remove());
        System.out.println(q.isEmpty());
    }
}