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【Java】随机队列

作者:mh942408056 / 发布于2014/4/11/ 678

随机队列

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

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

 private Item[] a;
 private int N;

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

 public int size() {
  return N;
 }

 public boolean isEmpty() {
  return N == 0;
 }

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

 }

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

 public Item sample() {

  randomSwap();
  return a[N-1];
 }

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

 private void randomSwap() {
  if(N<=1) return;
  Random rand = new Random();
  int swapIndex = rand.nextInt(N - 1);
  Item temp = a[N - 1];
  a[N - 1] = a[swapIndex];
  a[swapIndex] = temp;

 }

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

}

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　随机队列　

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