数据结构简单实现

import java.util.Iterator ;
import java.util.Scanner ;

public class ResizingArrayStack<Item> implements Iterable<Item>{
	private Item[] a = (Item[]) new Object[1] ;
	private int N = 0 ;
	
	public boolean isEmpty(){
		return N == 0 ;
	}
	
	public int size(){
		return N ;
	}

	private void resize(int max){
		Item[] temp = (Item[]) new Object[max] ;
		for (int i=0;i<N;i++) {
			temp[i] = a[i] ;
		}
		a = temp ;
	}

	public void push(Item item){
		if(N==a.length){
			resize(2*a.length) ;
		}
		a[N] = item ;
		N++ ;
	}

	public Item pop(){
		N-- ;
		Item item = a[N] ;
		a[N] = null ;
		if (N>0 && N==a.length/4) {
			resize(a.length/2) ;
		}
		return item ;
	}

	public Iterator<Item> iterator(){
		return new ReverseArrayIterator() ;
	}

	private class ReverseArrayIterator implements Iterator<Item>{
		private int i = N ;
		public boolean hasNext(){
			return i>0 ;
		}
		public Item next(){
			i-- ;
			return a[i] ;
		}
		public void remove(){

		}
	}

	public static void main(String[] args) {
		ResizingArrayStack<Integer> stack = new ResizingArrayStack<Integer>() ;
		System.out.println("please input the number of items:") ;
		Scanner sc = new Scanner(System.in) ;
		int n = sc.nextInt() ;
		for(int i=0;i<n;i++){
			stack.push(sc.nextInt()) ;
		}

		for(int i:stack){
			System.out.print(i + " ") ;
		}
		System.out.println() ;
	}
}

import java.util.Iterator ;
import java.util.Scanner ;

public class ListStack<Item> implements Iterable<Item>{
	private Node first ;
	private int N ;
	private class Node{
		Item item ;
		Node next ;
	}
	
	public boolean isEmpty(){
		return first == null ;
	}
	
	public int size(){
		return N ;
	}

	public void push(Item item){
		Node oldfirst = first ;
		first = new Node() ;
		first.item = item ;
		first.next = oldfirst ;
		N++ ;
	}

	public Item pop(){
		Item item = first.item ;
		first = first.next ;
		N-- ;
		return item ;
	}

	public Iterator<Item> iterator(){
		return new ListIterator() ;
	}
	private class ListIterator implements Iterator<Item>{
		private Node current = first ;
		public boolean hasNext(){
			return current != null ;
		}
		public Item next(){
			Item item = current.item ;
			current = current.next ;
			return item ;
		}
		public void remove(){

		}
	}

	public static void main(String[] args) {
		ListStack<Integer> stack = new ListStack<Integer>() ;
		System.out.println("please input the number of items:") ;
		Scanner sc = new Scanner(System.in) ;
		int n = sc.nextInt() ;
		for(int i=0;i<n;i++){
			stack.push(sc.nextInt()) ;
		}

		for(int i:stack){
			System.out.print(i + " ") ;
		}
		System.out.println() ;
	}
}

import java.util.Iterator ;
import java.util.Scanner ;

public class Queue<Item> implements Iterable<Item>{
	private Node first ;
	private Node last ;
	private int N ;
	
	private class Node{
		Item item ;
		Node next ;
	}
	
	public boolean isEmpty(){
		return first == null ;
	}
	
	public int size(){
		return N ;
	}
	
	public void enqueue(Item item){
		Node oldlast = last ;
		last = new Node() ;
		last.item = item ;
		last.next = null ;
		if (isEmpty()) {
			first = last ;
		}else{
			oldlast.next = last ;
		}
		N++ ;
	}
	
	public Item dequeue(){
		Item item = first.item ;
		first = first.next ;
		if (isEmpty()) {
			last = null ;
		}
		N-- ;
		return item ;
	}

	public Iterator<Item> iterator(){
		return new QueueIterator() ;
	}
	private class QueueIterator implements Iterator<Item>{
		private Node current = first ;
		public boolean hasNext(){
			return current!=null ;
		}
		public void remove(){

		}
		public Item next(){
			Item item = current.item ;
			current = current.next ;
			return item ;
		}
	}

	public static void main(String[] args) {
		Queue<String> q = new Queue<String>() ;
		System.out.println("please input the number of items:") ;
		Scanner sc = new Scanner(System.in) ;
		int n = sc.nextInt() ;
		for (int i=0;i<n;i++) {
			q.enqueue(sc.next()) ;
		}

		for (String s : q) {
			System.out.print(s + " ") ;
		}
		System.out.println() ;
	}
}

import java.util.Iterator ;
import java.util.Scanner ;

public class Bag<Item> implements Iterable<Item>{
	private Node first ;
	private int N = 0 ;

	private class Node{
		Item item ;
		Node next ;	
	}

	public void add(Item item){
		Node oldfirst = first ;
		first = new Node() ;
		first.item = item ;
		first.next = oldfirst ;
		N++ ;
	}

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

	public int size(){
		return N ;
	}

	public Iterator<Item> iterator(){
		return new ListIterator() ;
	}
	private class ListIterator implements Iterator<Item>{
		private Node current = first ;
		public boolean hasNext(){
			return current != null ;
		}
		public Item next(){
			Item item = current.item ;
			current = current.next ;
			return item ;
		}
		public void remove(){

		}
	}

	public static void main(String[] args) {
		Bag<Double> numbers = new Bag<Double>() ;
		System.out.println("please input the number of items:") ;
		Scanner sc = new Scanner(System.in) ;
		int n = sc.nextInt() ;
		for(int i=0;i<n;i++){
			numbers.add(sc.nextDouble()) ;
		}
		System.out.println("size(): " + numbers.size()) ;
		for (double d : numbers) {
			System.out.print(d + " ") ;
		}
		System.out.println() ;
	}
}