//背包节点类(布袋节点类) public class BagNode<Item>{ Item item; //参数 BagNode next; //下一个背包节点; }
import java.util.Iterator; //定义泛型背包类 public class Bag<Item> implements Iterable<Item> { //0定义私有的成员变量; private BagNode first; //1.定义添加背包项方法; public void add(Item item){ BagNode oldFirst=first; first.item=item; first.next=oldFirst; } @Override public Iterator<Item> iterator() { return new BagIterator(); } //定义私有的内部类; private class BagIterator implements Iterator<Item>{ BagNode node=first;//定义背包第一个节点是first @Override public boolean hasNext() { return node.next!=null; } @Override public Item next() { Item item=(Item)node.item; node=node.next; return item; } @Override public void remove() { //背包数据结构不存在删除方法,所以去掉该方法的定义。 } } }
附上:Robert Sedgewick的源码:可以看到高校立现,佩服!!!
import java.util.Iterator; import java.util.NoSuchElementException; public class Bag<Item> implements Iterable<Item> { private Node<Item> first; // beginning of bag private int n; // number of elements in bag // helper linked list class private static class Node<Item> { private Item item; private Node<Item> next; } /** * Initializes an empty bag. */ public Bag() { first = null; n = 0; } /** * Returns true if this bag is empty. * * @return {@code true} if this bag is empty; * {@code false} otherwise */ public boolean isEmpty() { return first == null; } /** * Returns the number of items in this bag. * * @return the number of items in this bag */ public int size() { return n; } /** * Adds the item to this bag. * * @param item the item to add to this bag */ public void add(Item item) { Node<Item> oldfirst = first; first = new Node<Item>(); first.item = item; first.next = oldfirst; n++; } /** * Returns an iterator that iterates over the items in this bag in arbitrary order. * * @return an iterator that iterates over the items in this bag in arbitrary order */ public Iterator<Item> iterator() { return new ListIterator<Item>(first); } // an iterator, doesn't implement remove() since it's optional private class ListIterator<Item> implements Iterator<Item> { private Node<Item> current; public ListIterator(Node<Item> first) { current = first; } public boolean hasNext() { return current != null; } public void remove() { throw new UnsupportedOperationException(); } public Item next() { if (!hasNext()) throw new NoSuchElementException(); Item item = current.item; current = current.next; return item; } } /** * Unit tests the {@code Bag} data type. * * @param args the command-line arguments */ public static void main(String[] args) { Bag<String> bag = new Bag<String>(); while (!StdIn.isEmpty()) { String item = StdIn.readString(); bag.add(item); } StdOut.println("size of bag = " + bag.size()); for (String s : bag) { StdOut.println(s); } } }
//背包的典型用例
public class Stats { public static void main(String[] args) { Bag<Double>numbers=new Bag<Double>(); //while(!StdIn.isEmpty()) for(int i=0;i<5;i++) numbers.add(StdIn.readDouble()); int N=numbers.size(); System.out.println(N); double sum=0.0; for(double x:numbers) sum+=x; double mean=sum/N; sum=0.0; for(double x:numbers) sum+=(x-mean)*(x-mean); double std=Math.sqrt(sum/(N-1)); StdOut.printf("Mean: %.2f\n",mean); StdOut.printf("Std dev:%.2f\n",std); } }利用背包求出平均值和样本标准差。