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【Java】随机背包

作者:mh942408056 / 发布于2014/4/11/ 765

随机背包

import java.util.Iterator;
import java.util.Random;

public class RandomBag<Item> implements Iterable<Item> {

 private Item[] a;
 private int N;

 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 RandomBag() {
  a = (Item[]) new Object[1];
  N = 0;
 }

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

 @Override
 public Iterator<Item> iterator() {
  // TODO Auto-generated method stub
  return new RandomBagIterator();
 }

 private class RandomBagIterator implements Iterator<Item> {
  private int i = 0;
  private Random rand = new Random();

  public RandomBagIterator() {
   randomSort();
  }

  private void randomSort() {
   for (int i = 0; i < N; i++) {
    int randomIndex = i + rand.nextInt(N - i);
    Item item = a[i];
    a[i] = a[randomIndex];
    a[randomIndex] = item;
   }

  }

  @Override
  public boolean hasNext() {
   // TODO Auto-generated method stub
   return i < N;
  }

  @Override
  public Item next() {
   // TODO Auto-generated method stub
   return a[i++];
  }

  @Override
  public void remove() {
   // TODO Auto-generated method stub

  }

 }

}

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