红包算法

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.*;

/**
* 红包
* 采用二倍均值算法
* (0.01, (X/Y) *2)
*/
public class RedEnvelope {
	
	// 最小可领取的金额
	private BigDecimal minAmount;
	
	// 最佳金额
	private BigDecimal bestAmount;
	
	// 总金额
	private BigDecimal totalAmount;
	
	// 总领取数量
	private Integer number;
	
	// 当前已经领取数量
	private Integer currentNumber;
	
	// 默认最小领取金额（单位:元）
	private final static BigDecimal MIN_AMOUNT_DEFAULT = BigDecimal.valueOf(0.01);
	
	// 金额领取池
	private List<BigDecimal> amountPool;
	
	/**
	* 设置最小领取金额
	* @param minAmount
	*/
	public void setMinAmount(BigDecimal minAmount) {
		this.minAmount = minAmount;
	}
	  
	
	/**
	* @param totalAmount 总金额
	* @param number 红包数量
	*/
	public RedEnvelope(BigDecimal totalAmount, Integer number) {
		this.totalAmount = totalAmount;
		this.number = number;
		this.currentNumber = 0;
		this.amountPool = new ArrayList<>();
		this.minAmount = MIN_AMOUNT_DEFAULT;
		this.bestAmount = BigDecimal.ZERO;
	}
	
	/**
	* 检查红包配置是否正确
	* throw RedEnvelopeException
	* @return true 正确 false 有误
	*/
	public void checkConfig() {
		// 检查总金额是否有效
		if (this.totalAmount == null || this.totalAmount.compareTo(BigDecimal.ZERO) != 1) {
			throw new RedEnvelopeException("RedEnvelope total amount must greater than 0");
		}
		// 检查总数量是否有效
		if (this.number == null || this.number.compareTo(0) != 1) {
			throw new RedEnvelopeException("RedEnvelope total amount must greater than 0");
		}
		// 检查最小领取金额是否有效
		if (this.minAmount.compareTo(MIN_AMOUNT_DEFAULT) == -1) {
			throw new RedEnvelopeException("RedEnvelope min amount must greater than or equal to " + MIN_AMOUNT_DEFAULT);
		}
		// 检查是否可分配
		if (this.minAmount.multiply(BigDecimal.valueOf(this.number)).compareTo(this.totalAmount) == 1) {
			throw new RedEnvelopeException("RedEnvelope unable to allocate");
		}
	}
	
	/**
	* 是否可以领取下一个
	* @return true 可以领取 false 不可以领取
	*/
	public Boolean hasNext() {
		return this.currentNumber < this.number;
	}
	
	private void execute() {
		final Random random = new Random();
		BigDecimal remainAmount = BigDecimal.valueOf(this.totalAmount.doubleValue());
		for (int i = this.number; i > 0; i--) {
		BigDecimal amount;
		if (i == 1) {
			amount = remainAmount;
		} else {
			// 计算可领取的最大范围值
			BigDecimal max = this.totalAmount.divide(BigDecimal.valueOf(this.number), 2, RoundingMode.HALF_UP).multiply(BigDecimal.valueOf(2));
			max = max.add(MIN_AMOUNT_DEFAULT).subtract(this.minAmount);
			// 计算公约
			BigDecimal convertRandom = BigDecimal.ONE.divide(this.minAmount, 10, RoundingMode.HALF_UP);
			Integer randomAmount = random.nextInt(convertRandom.multiply(max).intValue());
			amount = BigDecimal.valueOf(randomAmount).divide(convertRandom, 2, RoundingMode.HALF_DOWN);
			amount = BigDecimal.valueOf(Math.max(amount.doubleValue(), this.minAmount.doubleValue()));
			}
			bestAmount = BigDecimal.valueOf(Math.max(amount.doubleValue(), this.bestAmount.doubleValue()));
			// 将领取金额放入金额池
			amountPool.add(amount);
			// 剩余金额减少
			remainAmount = remainAmount.subtract(amount);
		}
	}
	
	/**
	* 获取当前红包信息
	*/
	public Info getInfo() {
		Info info = new Info();
		info.bestAmount = this.bestAmount;
		info.minAmount = this.minAmount;
		info.currentNumber = this.currentNumber;
		info.number = this.number;
		info.totalAmount = this.totalAmount;
		return info;
	}
	
	/**
	* 领取下一个红包
	* throw RedEnvelopeException
	* @return 领取到的金额
	*/
	public BigDecimal next() {
		if (amountPool.size() == 0) {
			checkConfig();
			execute();
		}
		if (hasNext()) {
			BigDecimal nextAmount = amountPool.get(this.currentNumber);
			this.currentNumber++;
			return nextAmount;
		}
		throw new RedEnvelopeException("RedEnvelope already end");
	}
	
	static class RedEnvelopeException extends RuntimeException {
		public RedEnvelopeException(String message) {
			super(message);
		}
	}
	
	static class Info {
	
		private BigDecimal totalAmount;
		private Integer number;
		private Integer currentNumber;
		private BigDecimal minAmount;
		private BigDecimal bestAmount;
		
		public BigDecimal getTotalAmount() {
			return totalAmount;
		}
		
		public Integer getNumber() {
			return number;
		}
		
		public Integer getCurrentNumber() {
			return currentNumber;
		}
		
		public BigDecimal getMinAmount() {
			return minAmount;
		}
		
		public BigDecimal getBestAmount() {
			return bestAmount;
		}
	
		@Override
		public String toString() {
			return "Info{" +
			"totalAmount=" + totalAmount +
			", number=" + number +
			", currentNumber=" + currentNumber +
			", minAmount=" + minAmount +
			", bestAmount=" + bestAmount +
			'}';
		}
	}
}