根据权重获取随机值

     有一组优惠 A－20优惠， B－30元优惠， C－5元优惠  当用户满足条件时随机返回一个优惠；在活动预算一定的情况下需要保证C类优惠券中奖概率最高，B类优惠券最低；以下是权重的实现；    

/**
* Copyright 2014-2015, , Inc. All Rights Reserved.
*
* Date: 2016年1月23日
*/
package org.demo.core;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
/***
*
* Desc:TODO
*
* @author zhangwei<wei.zw@corp.netease.com>
* @since 2016年1月23日 下午1:35:16
* @version v 0.1
*/
public class WeightRandomTest {
private static Map<Double, String> weightMapping = new HashMap<>();
static {
weightMapping.put(30d, "A");
weightMapping.put(20D, "B");
weightMapping.put(50D, "C");
}
public static void main(String[] args) {
int c = 0;
int a = 0;
int b = 0;
for (int i = 0; i < 2000000; i++) {
String str = WeightRandomUtil.getWeightRandom(weightMapping);
if ("A".equals(str)) {
a++;
} else if ("B".equals(str)) {
b++;
} else if ("C".equals(str)) {
c++;
}
}
System.out.println(c / 2000000d);
System.out.println(b / 2000000d);
System.out.println(a / 2000000d);
}
}
class WeightRandomUtil {
/***
* 计算权重总和
*
* @param weightArrays
* @return
* @author zhangwei<wei.zw@corp.netease.com>
*/
private static double weightSum(Set<Double> weights) {
double weightSum = 0;
for (double weightValue : weights) {
weightSum += weightValue;
}
return weightSum;
}
/***
*
*
* @param weightArrays
*
权重数组
* @return 返回数据
* @author zhangwei<wei.zw@corp.netease.com>
* @param <T>
*/
public static <T> T getWeightRandom(Map<Double, T> weightValueMapping) {
double weightSum = weightSum(weightValueMapping.keySet());
double stepWeightSum = 0;
List<Double> list = new ArrayList<>(weightValueMapping.keySet());
Collections.sort(list, new Comparator<Double>() {
@Override
public int compare(Double o1, Double o2) {
return (int) (o2 - o1);
}
});
double r = Math.random();
for (double weight : list) {
// 计算权重值
stepWeightSum += weight;
// 如果随机数落在了权重区间则返回索引值
if (r <= stepWeightSum / weightSum) {
return weightValueMapping.get(weight);
}
}
return null;
}
}