抢红包算法的实现
抢红包算法，不能是完全的根据总金额大小来随机计算。这样的话先抢的人很大几率一定会比后抢的人金额大。参考了网上的一些资料自己实现了一下。
参考
实现
import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;
import java.util.Random;
class Packet {
// 总金额
private int totalAmount;
// 总个数
private int totalCount;
public Packet(int totalAmount, int totalCount) {
assert totalAmount > 0;
assert totalCount > 0;
this.totalAmount = totalAmount;
this.totalCount = totalCount;
}
public int getTotalAmount() {
return totalAmount;
}
public void setTotalAmount(int totalAmount) {
this.totalAmount = totalAmount;
}
public int getTotalCount() {
return totalCount;
}
public void setTotalCount(int totalCount) {
this.totalCount = totalCount;
}
}
public class Main {
public static void main(String[] args) {
System.out.println(Integer.MAX_VALUE);
Random random = new Random();
for(int x = 0 ;x < 100 ;x ++){
test(random.nextInt(1000), random.nextInt(20) + 1);
}
}
public static void test(int totalAmount, int totalCount){
BigDecimal bigDecimal = new BigDecimal(0);
Packet packet = new Packet(totalAmount, totalCount);
System.out.print("[");
for (int x = 0 ;x < totalCount ;x ++){
int value = unpacking(packet);
bigDecimal = bigDecimal.add(new BigDecimal(value));
if (x != 0){
System.out.print(", ");
}
System.out.print(value);
}
System.out.println("] totalAmount=" + totalAmount + ",totalCount=" + totalCount+ ", accuracy=" + (bigDecimal.intValue() == totalAmount));
}
public static int unpacking(Packet packet){
if (packet.getTotalCount() == 1){
// 最后一个红包
int totalAmount = packet.getTotalAmount();
packet.setTotalAmount(0);
packet.setTotalCount(0);
return totalAmount;
}else if(packet.getTotalCount() == 0){
// 红包已经领取完
return 0;
}
// 最大金额 = (总金额 / 总个数)(四舍五入掉小数) * 2
BigDecimal totalAmount = new BigDecimal(packet.getTotalAmount());
BigDecimal maxValue = totalAmount.divide(new BigDecimal(packet.getTotalCount()),0 , RoundingMode.HALF_UP).multiply(new BigDecimal(2));
// 0% - 100% 随机概率
BigDecimal random = new BigDecimal(new Random().nextInt(101)).divide(new BigDecimal(100),2, RoundingMode.UNNECESSARY);
// 随机获取金额(四舍五入掉小数位)
int randomValue = maxValue.multiply(random, MathContext.UNLIMITED).intValue();
// 最小可以获取到1分
randomValue = randomValue < 1 ? 1 : randomValue;
// 修改数据
packet.setTotalAmount(packet.getTotalAmount() - randomValue);
packet.setTotalCount(packet.getTotalCount() - 1);
return randomValue;
}
}