隨機紅包算法，每個人都有自己的實現思路。
package com.jmmq.load.jim.algorithm;
import JAVA.math.BigDecimal;
import java.util.Arrays;
import java.util.List;
import java.util.Random;
/**
* 紅包算法
*/
public class RedPacketPrc {
private static final BigDecimal MIN = new BigDecimal("0.01");
public static void main(String[] args) {
String[] rs = redPacketRandom(new BigDecimal(1), 100, false);
BigDecimal sum = BigDecimal.ZERO;
for(String str: rs){
System.out.println(str);
sum = sum.add(new BigDecimal(str));
}
System.out.println("sum:" + sum);
System.out.println("(¯`•._.• •._.•´¯)(¯`•¸•´¯) (¯`•._.• •._.•´¯)(¯`•¸•´¯) (¯`•._.• •._.•´¯)(¯`•¸•´¯)");
String[] res = redPacketOpen(new BigDecimal(20), 6, false);
BigDecimal sum2 = BigDecimal.ZERO;
for(String str: res){
System.out.println(str);
sum2 = sum2.add(new BigDecimal(str));
}
System.out.println("sum2:" + sum2);
}
/**
*
* @param faceValue 面值 單位：元
* @param amount 人數
* @param avgFlag 是否平均
* @return
* 平均分就不寫了
* 思路一：
* 按百分比進行隨機計算，最后一個進行匝差計算
*/
public static String[] redPacketRandom(BigDecimal faceValue, int amount, boolean avgFlag){
// 先計算平均數 四舍五入
BigDecimal perValue = faceValue.divide(new BigDecimal(amount),3, BigDecimal.ROUND_HALF_UP);
// 平均下來最小的紅包必須大于等于 1分錢
if(perValue.compareTo(MIN) == -1){
throw new RuntimeException("red packet amount OutOfBounds min = 0.01");
}
String[] rs = new String[amount];
// 平均
if(avgFlag){
// 這里四舍五入重新計算
perValue = faceValue.divide(new BigDecimal(amount),2, BigDecimal.ROUND_HALF_UP);
Arrays.fill(rs, perValue.toString());
// 無法除盡
if(perValue.multiply(new BigDecimal(amount)).compareTo(faceValue) != 0 ){
// 隨機獲取一個下標
int index = new Random().nextInt(amount);
rs[index] = String.valueOf(new BigDecimal(rs[index]).add(
faceValue.subtract(perValue.multiply(new BigDecimal(amount)))));
}
return rs;
}
BigDecimal weightSum = BigDecimal.ZERO;
BigDecimal redSum = BigDecimal.ZERO;
BigDecimal[] weights = new BigDecimal[amount];
// 隨機
for (int i=0; i<rs.length; i++){
BigDecimal seed = new BigDecimal(new Random().nextInt(amount));
weightSum = weightSum.add(seed);
weights[i] = seed;
// 循環最后一個后計算金額
if(i == rs.length -1){
for(int j=0; j<rs.length; j++){
// 修改為向下取值，這樣差額永遠都是正數就不存在吃不掉差額的問題了
BigDecimal val = faceValue.multiply(weights[j].divide(weightSum,2, BigDecimal.ROUND_HALF_UP));
if(val.compareTo(MIN) == -1){
val = MIN;
}
redSum = redSum.add(val);
rs[j] = val.toString();
}
}
}
BigDecimal diff = faceValue.subtract(redSum);
if(faceValue.compareTo(redSum) != 0){
// 找到第一個加上或減少diff大于MIN的元素修改金額
for(int i=0; i<rs.length; i++){
if(new BigDecimal(rs[i]).add(diff).compareTo(MIN) > -1 ){
rs[i] = new BigDecimal(rs[i]).add(diff).toString();
break;
}
}
}
// 若沒有任何一個元素能吃掉差額,因此差額需要進行分攤了，
// 這里簡單粗暴的將循環到大于MIN的都改為MIN同時減少差額
// 這里代碼不進行優化，會寫另外一個優化的算法
if(faceValue.compareTo(redSum) != 0){
for(int i=0; i<rs.length; i++){
if(new BigDecimal(rs[i]).compareTo(MIN) > 0){
if(new BigDecimal(rs[i]).add(diff).compareTo(MIN) > -1){
rs[i] = new BigDecimal(rs[i]).add(diff).toString();
break;
} else {
diff.add(new BigDecimal(rs[i])).subtract(MIN);
rs[i] = MIN.toString();
}
}
}
}
return rs;
}
/**
* 上面算法進行優化
* @param faceValue 面值 單位：元
* @param amount 人數
* @param avgFlag 是否平均
* @return
* 優化思路：
* 上面算法為了保證紅包最小金額處理上花費了大量的循環來處理
* 優化上就直接先分配最小金額，然后在進行隨機分攤剩余的錢
*/
public static String[] redPacketOpen(BigDecimal faceValue, int amount, boolean avgFlag){
// 先計算平均數 四舍五入
BigDecimal perValue = faceValue.divide(new BigDecimal(amount),3, BigDecimal.ROUND_HALF_UP);
// 平均下來最小的紅包必須大于等于 1分錢
if(perValue.compareTo(MIN) == -1){
throw new RuntimeException("red packet amount OutOfBounds min = 0.01");
}
String[] rs = new String[amount];
// 平均
if(avgFlag){
// 這里四舍五入重新計算
perValue = faceValue.divide(new BigDecimal(amount),2, BigDecimal.ROUND_HALF_UP);
Arrays.fill(rs, perValue.toString());
// 無法除盡
if(perValue.multiply(new BigDecimal(amount)).compareTo(faceValue) != 0 ){
// 隨機獲取一個下標
int index = new Random().nextInt(amount);
rs[index] = String.valueOf(new BigDecimal(rs[index]).add(
faceValue.subtract(perValue.multiply(new BigDecimal(amount)))));
}
return rs;
}
// 隨機
// 先把低保放進去
Arrays.fill(rs, MIN.toString());
BigDecimal weightSum = BigDecimal.ZERO;
BigDecimal redSum = BigDecimal.ZERO;
BigDecimal[] weights = new BigDecimal[amount];
// 隨機
for (int i=0; i<rs.length; i++){
BigDecimal seed = new BigDecimal(new Random().nextInt(amount));
weightSum = weightSum.add(seed);
weights[i] = seed;
// 循環最后一個后計算金額
if(i == rs.length -1){
for(int j=0; j<rs.length; j++){
BigDecimal val = faceValue.multiply(weights[j].divide(weightSum,2, BigDecimal.ROUND_DOWN));
redSum = redSum.add(val);
rs[j] = val.add(MIN).toString();
}
}
}
// 隨機獲取一個下標
BigDecimal diff = faceValue.subtract(redSum);
int index = new Random().nextInt(amount);
rs[index] = String.valueOf(new BigDecimal(rs[index]).add(diff));
return rs;
}
}
