链式栈、队列、背包

/*
    栈先进后出
*/
public class Stack
 
  {
    private Node first;
    private int N;
    private class Node{
        Iteam item;
        Node next;
    }
    public boolean isEmpty(){
        return first == null;
    }
    public int size(){
        return N;
    }
    public void push(Iteam item){
        Node oldfirst = first;
        first = new Node();
        first.item = item;
        first.next = oldfirst.item;
        N++;
    }
    public Iteam pop(){
        Iteam item = first.item;
        first = first.next;
        N--;
        return item;
    }
}

/*
    队列先进先出
*/
public class Queue
  
   { private Node first; private Node last; private int N; private class Node{ Iteam item; Node next; } public boolean isEmpty(){ return first == null; } public int size(){ return N; } public void enqueue(Iteam item){ Node oldlast = last; last = new Node(); last.item = item; last.next = null; if(isEmpty()) //如果队列为空则把尾结点（唯一的节点）作为头节点 first = last; else oldfirst.next = last; N++; } public Iteam dequeue(){ Iteam item = first.item; first = first.next; if(isEmpty()) last = null; N--; return item; } } /* 背包不关注顺序不支持单个删除 */ import java.util.Iterator; //导入迭代接口 public class Bag
   
     implements Iterable
    
     { private Node first; private class Node{ Iteam item; Node next; } public void add(Iteam item){ Node oldfirst = first; first = new Node(); first.item = item; first.next = oldfirst; } public Iterator
     
       Iterator(){ return new listIterator(); } private class listIterator implements Iterator
      
       { private Node current = first; public boolean hasNext(){ return current != null; } public void remove(){} public Iteam next(){ Iteam item = current.item; current = current.next; return item; } } }