算法学习之基础(背包 列队 栈) 习题1.3.34随机背包的实现

 1 package gh;
 2 
 3 import java.util.Iterator;
 4 /**
 5  * 随机背包
 6  * @author ganhang
 7  *
 8  * @param <T>
 9  */
10 public class RandomBag<T>implements Iterable<T> {
11     private int n;//元素数量
12     private T [] bag;
13     public RandomBag(int max){
14         bag=(T[])new Object[max];
15     }
16     public boolean isEmpty(){
17         return n==0;
18     }
19     
20     public int size(){
21         return n;
22     }
23     public void add(T item){
24         bag[n++]=item;
25     }
26 
27     @Override
28     public Iterator<T> iterator() {
29         // TODO Auto-generated method stub
30         return new RandomBagIterator();
31     }
32     private class RandomBagIterator implements Iterator<T>{
33         public RandomBagIterator(){
34             shuffle(bag);//构造函数中随机排列下数组中的元素
35         }
36         private void shuffle(T b[]){//数组的随机排序
37             int N=b.length;
38             for(int i=0;i<N;i++){
39                 int r=i+(int)(Math.random()*(N-i));
40                 T temp=b[i];
41                 b[i]=b[r];
42                 b[r]=temp;
43             }
44         }
45         @Override
46         public boolean hasNext() {
47             // TODO Auto-generated method stub
48             return n!=0;
49         }
50 
51         @Override
52         public T next() {
53             // TODO Auto-generated method stub
54             return bag[--n];
55         }
56 
57         @Override
58         public void remove() {
59             // TODO Auto-generated method stub
60             
61         }
62         
63     }
64     
65 }