add WeightListRandomSelector

hutool-core/src/main/java/org/dromara/hutool/core/lang/selector/WeightListRandomSelector.java

@@ -0,0 +1,155 @@
+/*
+ * Copyright (c) 2024 Hutool Team and hutool.cn
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.dromara.hutool.core.lang.selector;
+
+import org.dromara.hutool.core.lang.Assert;
+import org.dromara.hutool.core.util.ObjUtil;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+/**
+ * 动态按权重随机的随机池，底层是list实现。
+ * 原理为加入的{@link WeightObj}依次增加权重，随机时根据权重计算随机值，然后二分查找小于等于随机值的权重，返回对应的元素。<br>
+ * 我们假设随机池中有4个对象，其权重为4，5，1，6，权重越高，'-'越多，那么随机池如下：
+ * <pre>{@code
+ *     [obj1,  obj2, obj3, obj4  ]
+ *     [----, -----,  -  , ------]
+ * }</pre>
+ * 然后最后一个元素的权重值为总权重值，即obj2的权重值为obj1权重+obj2本身权重，依次类推。<br>
+ * 我们取一个总权重范围的随机数，根据随机数在'-'列表中的位置，找到对应的obj即随机到的对象。
+ *
+ * @param <E> 元素类型
+ * @author 王叶峰
+ */
+public class WeightListRandomSelector<E> implements Selector<E>, Serializable {
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * 随机元素池
+	 */
+	private final List<WeightObj<E>> randomPool;
+
+	/**
+	 * 构造
+	 */
+	public WeightListRandomSelector() {
+		randomPool = new ArrayList<>();
+	}
+
+	/**
+	 * 构造
+	 *
+	 * @param poolSize 初始随机池大小
+	 */
+	public WeightListRandomSelector(final int poolSize) {
+		randomPool = new ArrayList<>(poolSize);
+	}
+
+	/**
+	 * 增加随机种子
+	 *
+	 * @param e      随机对象
+	 * @param weight 权重
+	 */
+	public void add(final E e, final int weight) {
+		Assert.isTrue(weight > 0, "权重必须大于0！");
+		randomPool.add(new WeightObj<>(e, sumWeight() + weight));
+	}
+
+	/**
+	 * 移除随机种子
+	 *
+	 * @param e 随机对象
+	 * @return 是否移除成功
+	 */
+	public boolean remove(final E e) {
+		boolean removed = false;
+		int weight = 0;
+		int i = 0;
+		final Iterator<WeightObj<E>> iterator = randomPool.iterator();
+		WeightObj<E> ew;
+		while (iterator.hasNext()) {
+			ew = iterator.next();
+			if (!removed && ObjUtil.equals(ew.obj, e)) {
+				iterator.remove();
+				weight = ew.weight - (i == 0 ? 0 : randomPool.get(i - 1).weight);// 权重=当前权重-上一个权重
+				removed = true;
+			}
+			if (removed) {
+				// 重新计算后续权重
+				ew.weight -= weight;
+			}
+			i++;
+		}
+		return removed;
+	}
+
+	/**
+	 * 判断是否为空
+	 *
+	 * @return 是否为空
+	 */
+	public boolean isEmpty() {
+		return randomPool.isEmpty();
+	}
+
+	@Override
+	public E select() {
+		if (isEmpty()) {
+			return null;
+		}
+		if (randomPool.size() == 1) {
+			return randomPool.get(0).obj;
+		}
+		return binarySearch((int) (sumWeight() * Math.random()));
+	}
+
+	/**
+	 * 二分查找小于等于key的最大值的元素
+	 *
+	 * @param randomWeight 随机权重值，查找这个权重对应的元素
+	 * @return 随机池的一个元素或者null 当key大于所有元素的总权重时，返回null
+	 */
+	private E binarySearch(final int randomWeight) {
+		int low = 0;
+		int high = randomPool.size() - 1;
+
+		while (low <= high) {
+			final int mid = (low + high) >>> 1;
+			final int midWeight = randomPool.get(mid).weight;
+
+			if (midWeight < randomWeight) {
+				low = mid + 1;
+			} else if (midWeight > randomWeight) {
+				high = mid - 1;
+			} else {
+				return randomPool.get(mid).obj;
+			}
+		}
+		return randomPool.get(low).obj;
+	}
+
+	private int sumWeight() {
+		if (randomPool.isEmpty()) {
+			return 0;
+		}
+		return randomPool.get(randomPool.size() - 1).weight;
+	}
+}

hutool-core/src/main/java/org/dromara/hutool/core/lang/selector/WeightObj.java

@@ -29,7 +29,7 @@ public class WeightObj<T> {
 	/** 对象 */
 	protected T obj;
 	/** 权重 */
-	protected final int weight;
+	protected int weight;
 
 	/**
 	 * 构造

hutool-core/src/test/java/org/dromara/hutool/core/lang/selector/WeightListRandomSelectorTest.java

@@ -0,0 +1,77 @@
+package org.dromara.hutool.core.lang.selector;
+
+import org.dromara.hutool.core.date.DateUtil;
+import org.dromara.hutool.core.date.StopWatch;
+import org.dromara.hutool.core.lang.Console;
+import org.dromara.hutool.core.util.RandomUtil;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class WeightListRandomSelectorTest {
+
+	@Test
+	@Disabled
+	public void weightListRandomTest() {
+		final Map<Integer, Times> timesMap = new HashMap<>();
+		final int size = 100;
+		int sumWeight = 0;
+		final WeightListRandomSelector<Integer> pool = new WeightListRandomSelector<>(size);
+		for (int i = 0; i < size; i++) {
+			final int weight = RandomUtil.randomInt(1, 100);
+			pool.add(i, weight);
+			sumWeight += weight;
+			timesMap.put(i, new Times(weight));
+		}
+
+		final int times = 100000000;// 随机次数
+		for (int i = 0; i < times; i++) {
+			timesMap.get(pool.select()).num++;
+		}
+
+		final int finalSumWeight = sumWeight;
+		timesMap.forEach((key, times1) -> {
+			final double expected = times1.weight / finalSumWeight;// 期望概率
+			final double actual = (double) timesMap.get(key).num / times;// 真实随机概率
+			Console.log(expected, actual);
+		});
+	}
+
+	private static class Times {
+		int num;
+		double weight;
+
+		public Times(final double weight) {
+			this.weight = weight;
+		}
+	}
+
+	@Test
+	public void weightRandomBenchTest() {
+		final int size = 100;
+		final WeightListRandomSelector<Integer> pool = new WeightListRandomSelector<>(size);
+		final WeightRandomSelector<Integer> pool2 = new WeightRandomSelector<>();
+		for (int i = 0; i < size; i++) {
+			final int weight = RandomUtil.randomInt(1, 100);
+			pool.add(i, weight);
+			pool2.add(i, weight);
+		}
+
+		final int count = 1000;
+		final StopWatch stopWatch = DateUtil.createStopWatch();
+		stopWatch.start("WeightListRandomSelector");
+		for (int i = 0; i < count; i++) {
+			pool.select();
+		}
+		stopWatch.stop();
+		stopWatch.start("WeightRandomSelector");
+		for (int i = 0; i < count; i++) {
+			pool2.select();
+		}
+		stopWatch.stop();
+
+		//Console.log(stopWatch.prettyPrint());
+	}
+}