java實現計算最優現金優惠券組合

在眾多可疊加現金型別優惠券中（比如100減5,200減12等），選出可打折金額最大的組合。

下面程式碼

package com.dk.common.util.algo;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * 
 * 計算最優優惠券組合
 *
 */
public class CalcDiscountCouponOptimalCombination {

	/// ***** 測試
	public static void main(String[] args) {

		double max = 600;

		List<Item> list = new ArrayList<>();
		list.add(new Item(100, 2));
		list.add(new Item(100, 3));
		list.add(new Item(300, 3));
		list.add(new Item(300, 9));
		list.add(new Item(300, 4));
		list.add(new Item(200, 4));
		list.add(new Item(100, 2));
		list.add(new Item(200, 9));
		list.add(new Item(300, 4));
		list.add(new Item(100, 3));
		list.add(new Item(230, 3));

		list.add(new Item(300, 3));
		list.add(new Item(500, 9));
		list.add(new Item(300, 4));
		list.add(new Item(100, 4));
		list.add(new Item(100, 2));
		list.add(new Item(400, 9));
		list.add(new Item(300, 4));
		list.add(new Item(100, 3));
		list.add(new Item(230, 3));

		for (int i = 0; i < 5; i++) {
			list.add(new Item(300, 3));
			list.add(new Item(500, 9));
			list.add(new Item(300, 4));
			list.add(new Item(100, 4));
			list.add(new Item(100, 2));
			list.add(new Item(400, 9));
			list.add(new Item(300, 4));
			list.add(new Item(100, 3));
			list.add(new Item(230, 3));
			list.add(new Item(230, 3));
		}

		// ************************

		// 券數量多的，建議先按“折扣限制”從大到小排序，可以減少邏輯計算時間
		list.sort((o1, o2) -> o1.deduct == o2.deduct ? 0 : o1.deduct > o2.deduct ? -1 : 1);

		Map<String, Double> maxReduceIdxIssMap = calcMaxReduceIdxIssMap(list, max);
		System.out.println(maxReduceIdxIssMap);

		for (String idxIss : maxReduceIdxIssMap.keySet()) {
			System.out.println("-------------------------------------");
			System.out.println(idxIss);

			String[] idxIsArr = idxIss.split("");
			for (int idx = 0; idx < idxIsArr.length; idx++) {
				String is = idxIsArr[idx];
				if ("1".equals(is)) {
					System.out.println(idx + ": " + list.get(idx));
				}
			}

		}

	}

	/**
	 * 計算最大優惠組合列表
	 */
	public static Map<String, Double> calcMaxReduceIdxIssMap(List<Item> list, double maxAstrict) {
		Map<String, Double> maxReduceIdxIssMap = new HashMap<>();// 統計極限組合

		int len = list.size();
		LoopRear lr = new LoopRear() {
			double currMaxReduce = 0;

			// idxIss 由0、1組成，1所在下標表示對應項參與了此組合
			@Override
			public boolean runRear(int start, String idxIss, double deductSum, double reduceSum) {
				boolean haveRear = false;// 後面流程有沒有符合條件的子類組合
				String pad = "1";
				for (int i = start; i < len; i++) {
					Item item = list.get(i);
					double currDeductSum = deductSum + item.deduct;// 當前組合折扣限制總和
					double currReduceSum = reduceSum + item.reduce;// 當前組合折扣額度總和
					if (currDeductSum <= maxAstrict) {
						haveRear = true;// 當前組合限制總和小於總金額，表示當前組合的父類不是極限組合（存在子類組合）
						String currIdxIss = idxIss + pad;
						boolean haveRearRear = this.runRear(i + 1, currIdxIss, currDeductSum, currReduceSum);// 是否存在子類組合
						if (!haveRearRear) {
							// 不存在子類組合，表示當前組合為一個極限組合
							// 比對之前的折扣金額，只保留最大折扣金額的
							if (currReduceSum > currMaxReduce) {
								currMaxReduce = currReduceSum;
								maxReduceIdxIssMap.clear();
								maxReduceIdxIssMap.put(currIdxIss, currReduceSum);
							} else if (currReduceSum == currMaxReduce) {
								maxReduceIdxIssMap.put(currIdxIss, currReduceSum);
							}
						}
					}
					pad = "0" + pad;// 前面下標的項不參與之後組合，後移一位
				}
				return haveRear;
			}
		};
		lr.runRear(0, "", 0, 0);// 從第一個開始執行

		return maxReduceIdxIssMap;
	}

	public static class Item {
		protected double deduct;// 折扣限制，折扣條件
		protected double reduce;// 折扣額度

		public Item(double deduct, double reduce) {
			super();
			this.deduct = deduct;
			this.reduce = reduce;
		}

		@Override
		public String toString() {
			return reduce + "[" + deduct + "]";
		}
	}

	protected interface LoopRear {
		boolean runRear(int start, String idxIss, double deductSum, double reduceSum);
	}

}