com.neko233.toolchain.common.random.WeightRandom Maven / Gradle / Ivy
package com.neko233.toolchain.common.random;
import com.neko233.toolchain.common.base.MapUtils233;
import com.neko233.toolchain.common.base.RandomUtils233;
import java.io.Serializable;
import java.util.Random;
import java.util.SortedMap;
import java.util.TreeMap;
/**
* 权重随机算法实现
*
* 平时，经常会遇到权重随机算法，从不同权重的N个元素中随机选择一个，并使得总体选择结果是按照权重分布的。如广告投放、负载均衡等。
*
*
* 如有4个元素A、B、C、D，权重分别为1、2、3、4，随机结果中A:B:C:D的比例要为1:2:3:4。
*
* 总体思路：累加每个元素的权重A(1)-B(3)-C(6)-D(10)，则4个元素的的权重管辖区间分别为[0,1)、[1,3)、[3,6)、[6,10)。
* 然后随机出一个[0,10)之间的随机数。落在哪个区间，则该区间之后的元素即为按权重命中的元素。
*
*
* 参考博客：https://www.cnblogs.com/waterystone/p/5708063.html
*
*
* @param 权重随机获取的对象类型
* @author looly
* @since 3.3.0
*/
public class WeightRandom implements Serializable {
private static final long serialVersionUID = -8244697995702786499L;
private final TreeMap weightMap;
/**
* 构造
*/
public WeightRandom() {
weightMap = new TreeMap<>();
}
// ---------------------------------------------------------------------------------- Constructor start
/**
* 构造
*
* @param weightObject 带有权重的对象
*/
public WeightRandom(WeightObject weightObject) {
this();
if (null != weightObject) {
add(weightObject);
}
}
/**
* 构造
*
* @param weightObjs 带有权重的对象
*/
public WeightRandom(Iterable> weightObjs) {
this();
if (weightObjs == null) {
return;
}
for (WeightObject weightObject : weightObjs) {
add(weightObject);
}
}
/**
* 构造
*
* @param weightObjects 带有权重的对象
*/
public WeightRandom(WeightObject[] weightObjects) {
this();
for (WeightObject weightObject : weightObjects) {
add(weightObject);
}
}
/**
* 创建权重随机获取器
*
* @param 权重随机获取的对象类型
* @return {@link WeightRandom}
*/
public static WeightRandom create() {
return new WeightRandom<>();
}
// ---------------------------------------------------------------------------------- Constructor end
/**
* 增加对象
*
* @param obj 对象
* @param weight 权重
* @return this
*/
public WeightRandom add(T obj, double weight) {
return add(new WeightObject<>(obj, weight));
}
/**
* 增加对象权重
*
* @param weightObject 权重对象
* @return this
*/
public WeightRandom add(WeightObject weightObject) {
if (null != weightObject) {
final double weight = weightObject.getWeight();
if (weightObject.getWeight() > 0) {
double lastWeight = (this.weightMap.size() == 0) ? 0 : this.weightMap.lastKey();
this.weightMap.put(weight + lastWeight, weightObject.getObj());// 权重累加
}
}
return this;
}
/**
* 清空权重表
*
* @return this
*/
public WeightRandom clear() {
if (null != this.weightMap) {
this.weightMap.clear();
}
return this;
}
/**
* 下一个随机对象
*
* @return 随机对象
*/
public T next() {
if (MapUtils233.isEmpty(this.weightMap)) {
return null;
}
final Random random = RandomUtils233.getRandom();
final double randomWeight = this.weightMap.lastKey() * random.nextDouble();
final SortedMap tailMap = this.weightMap.tailMap(randomWeight, false);
return this.weightMap.get(tailMap.firstKey());
}
}