前言今天下午做了拼多多在牛客网上的在线笔试题，感觉自己的智商被鄙视到了···不过其中一道题的某一部分引起了我极大的兴趣，感觉可以总结一下，做好积累~题目的部分我拍照如下所示

这里面最复杂的就是第3点，对秒杀活动进行排序，排序条件多，排序条件使用各不相同，在笔试中给我带来了很大的困扰，最后当然也是没做完啦····
解决方案吃完晚饭开始寻找解决方法，觉得应该会很有意思，果然看到了比较好的做法，链接在这
java多条件优先级排序 — Comparator这个方案以我这样几个月的菜鸟看来，最巧妙的就是把 多个比较器 Comparator放进一个 比较器列表 中，然后在需要时，在new一个比较器，然后在其中foreach使用各个比较器，而且注意看他代码24行的if，没有在循环中间返回结果为0的情况，而是在使用完所有比较器最后再返回0；这样就能按顺序依次使用各个比价器了。那么回到我的题目中来
我先定义了4个比较器，分别用于4中不同项目的排序比较//按人气从大到小对活动进行排序private Comparator<Activity> renqiComparator = new Comparator<Activity>() {@Overridepublic int compare(Activity o1, Activity o2) {if(goods.get(o1.goodsId).renQi == goods.get(o2.goodsId).renQi) {return 0;} else {return goods.get(o1.goodsId).renQi > goods.get(o2.goodsId).renQi ? -1 : 1;}}};//按商品id从小到大排序private Comparator<Activity> idComparator = new Comparator<Activity>() {@Overridepublic int compare(Activity o1, Activity o2) {if(o1.goodsId == o2.goodsId) {return 0;} else {return o1.goodsId > o2.goodsId ? 1 : -1;}}};//按活动开始时间从早到晚排序private Comparator<Activity> startTimeComparator = new Comparator<Activity>() {@Overridepublic int compare(Activity o1, Activity o2) {if(o1.startTime == o2.startTime) {return 0;} else {return o1.startTime > o2.startTime ? 1 :-1;}}};//按活动的最后卖出时间从晚到早排序private Comparator<Activity> sellTimeComparator = new Comparator<Activity>() {@Overridepublic int compare(Activity o1, Activity o2) {if(o1.sellTime == o2.sellTime) {return 0;} else {return o1.sellTime > o2.sellTime ? -1 : 1;}}};
然后定义了三个比较器列表，分别用于三种情况下的比较，然后在构造器中初始化这3个比较器列表public Main3() {//在构造器中把这个复杂的比较器列表进行初始化//对于进行中（未售罄）的活动，按商品人气从高到低、商品ID从小到大排序
        activityComparatorList1.add(renqiComparator);activityComparatorList1.add(idComparator);//对于进行中（已售罄）的活动，按最后卖出时间从晚到早、商品人气从高到低、商品ID从小到大排序
        activityComparatorList2.add(sellTimeComparator);activityComparatorList2.add(renqiComparator);activityComparatorList2.add(idComparator);//对于未开始的活动，依次按开始时间从早到晚、商品人气从高到低、商品ID从小到大排序
        activityComparatorList3.add(startTimeComparator);activityComparatorList3.add(renqiComparator);activityComparatorList3.add(idComparator);}
最后再需要对活动排序的地方这样使用，针对不同阶段使用不同的比较器列表。Collections.sort(list, new Comparator<Activity>() {@Overridepublic int compare(Activity o1, Activity o2) {//在同一阶段内的比较if(o1.limitQuantity>0 && o2.limitQuantity>0) {//进行中未售罄for(Comparator<Activity> comparator : activityComparatorList1) {if(comparator.compare(o1, o2) < 0) {return -1;} else if(comparator.compare(o1, o2) > 0) {return 1;}}return 0; //关键在这，里面的比较器给出0时不处理，指导全部比较完成都相等的情况下才给出0
} else if(o1.limitQuantity == 0 && o2.limitQuantity == 0) {//进行中已售罄for(Comparator<Activity> comparator : activityComparatorList2) {if(comparator.compare(o1, o2) < 0) {return -1;} else if(comparator.compare(o1, o2) > 0) {return 1;}}return 0; //关键在这，里面的比较器给出0时不处理，指导全部比较完成都相等的情况下才给出0
} else if(o1.startTime>time && o2.startTime>time) { //未开始活动for(Comparator<Activity> comparator : activityComparatorList3) {if(comparator.compare(o1, o2) < 0) {return -1;} else if(comparator.compare(o1, o2) > 0) {return 1;}}return 0; //关键在这，里面的比较器给出0时不处理，指导全部比较完成都相等的情况下才给出0
                }//在不同阶段的比较if(o1.limitQuantity > 0 && (o2.limitQuantity == 0 || o2.startTime>time)) {return -1;} else if(o1.limitQuantity == 0 && o2.startTime>time) {return -1;} else {return 1;}}});
这样我感觉是比较合理的解决了这样一个多重不同条件的比较问题，而且感觉没有使用过多的判断使得逻辑混乱。
附全部代码这道题最后也没有放在OJ上测试过，所以可能有错，仅供参考package com.pinduoduo;import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Scanner;public class Main3 {public HashMap<Integer, Good> goods = new HashMap<>();public ArrayList<Activity> activities = new ArrayList<>();public List<Comparator<Activity>> activityComparatorList1 = new ArrayList<>();public List<Comparator<Activity>> activityComparatorList2 = new ArrayList<>();public List<Comparator<Activity>> activityComparatorList3 = new ArrayList<>();//按人气从大到小对活动进行排序private Comparator<Activity> renqiComparator = new Comparator<Activity>() {@Overridepublic int compare(Activity o1, Activity o2) {if(goods.get(o1.goodsId).renQi == goods.get(o2.goodsId).renQi) {return 0;} else {return goods.get(o1.goodsId).renQi > goods.get(o2.goodsId).renQi ? -1 : 1;}}};//按商品id从小到大排序private Comparator<Activity> idComparator = new Comparator<Activity>() {@Overridepublic int compare(Activity o1, Activity o2) {if(o1.goodsId == o2.goodsId) {return 0;} else {return o1.goodsId > o2.goodsId ? 1 : -1;}}};//按活动开始时间从早到晚排序private Comparator<Activity> startTimeComparator = new Comparator<Activity>() {@Overridepublic int compare(Activity o1, Activity o2) {if(o1.startTime == o2.startTime) {return 0;} else {return o1.startTime > o2.startTime ? 1 :-1;}}};//按活动的最后卖出时间从晚到早排序private Comparator<Activity> sellTimeComparator = new Comparator<Activity>() {@Overridepublic int compare(Activity o1, Activity o2) {if(o1.sellTime == o2.sellTime) {return 0;} else {return o1.sellTime > o2.sellTime ? -1 : 1;}}};public Main3() {//在构造器中把这个复杂的比较器列表进行初始化//对于进行中（未售罄）的活动，按商品人气从高到低、商品ID从小到大排序
        activityComparatorList1.add(renqiComparator);activityComparatorList1.add(idComparator);//对于进行中（已售罄）的活动，按最后卖出时间从晚到早、商品人气从高到低、商品ID从小到大排序
        activityComparatorList2.add(sellTimeComparator);activityComparatorList2.add(renqiComparator);activityComparatorList2.add(idComparator);//对于未开始的活动，依次按开始时间从早到晚、商品人气从高到低、商品ID从小到大排序
        activityComparatorList3.add(startTimeComparator);activityComparatorList3.add(renqiComparator);activityComparatorList3.add(idComparator);}public int addActivity(int startTime, int endTime, int goodsId, int limitQuantity) {if(limitQuantity <= goods.get(goodsId).kuCun) {Activity activity = new Activity();activity.startTime = startTime;activity.endTime = endTime;activity.goodsId = goodsId;activity.limitQuantity = limitQuantity;activity.id = activities.size();activities.add(activity);return activity.id;}return -1;}public int buyGoods(int time, int activityId, int quantity) {Activity activity = activities.get(activityId);int startTime = activity.startTime;int endTime = activity.endTime;int limitQuantity = activity.limitQuantity;if(time < startTime || time >= endTime) {return -1;} else if(quantity > limitQuantity) {return -1;} else {activity.limitQuantity -= quantity;activity.sellTime = time;return 0;}}public List<Activity> getActivityList(int time) {ArrayList<Activity> list = new ArrayList<>();for (Activity activity : activities) {if(time >= activity.startTime && time < activity.endTime) {list.add(activity);}}Collections.sort(list, new Comparator<Activity>() {@Overridepublic int compare(Activity o1, Activity o2) {//在同一阶段内的比较if(o1.limitQuantity>0 && o2.limitQuantity>0) {//进行中未售罄for(Comparator<Activity> comparator : activityComparatorList1) {if(comparator.compare(o1, o2) < 0) {return -1;} else if(comparator.compare(o1, o2) > 0) {return 1;}}return 0; //关键在这，里面的比较器给出0时不处理，指导全部比较完成都相等的情况下才给出0
} else if(o1.limitQuantity == 0 && o2.limitQuantity == 0) {//进行中已售罄for(Comparator<Activity> comparator : activityComparatorList2) {if(comparator.compare(o1, o2) < 0) {return -1;} else if(comparator.compare(o1, o2) > 0) {return 1;}}return 0; //关键在这，里面的比较器给出0时不处理，指导全部比较完成都相等的情况下才给出0
} else if(o1.startTime>time && o2.startTime>time) { //未开始活动for(Comparator<Activity> comparator : activityComparatorList3) {if(comparator.compare(o1, o2) < 0) {return -1;} else if(comparator.compare(o1, o2) > 0) {return 1;}}return 0; //关键在这，里面的比较器给出0时不处理，指导全部比较完成都相等的情况下才给出0
                }//在不同阶段的比较if(o1.limitQuantity > 0 && (o2.limitQuantity == 0 || o2.startTime>time)) {return -1;} else if(o1.limitQuantity == 0 && o2.startTime>time) {return -1;} else {return 1;}}});return list;}public static void main(String[] args) {Scanner sc = new Scanner(System.in);Main3 main = new Main3();int n = sc.nextInt();int m = sc.nextInt();for(int i=0; i<n; i++) {Good good = new Good();good.id = sc.nextInt();good.renQi = sc.nextInt();good.kuCun = sc.nextInt();main.goods.put(good.id, good);}sc.nextLine();String[] ask = new String[m];for(int i=0; i<m; i++) {ask[i] = sc.nextLine();}for(int i=0; i<m; i++) {String[] command = ask[i].split(" ");if("add".equals(command[1])) {int time = Integer.parseInt(command[0]);int startTime = Integer.parseInt(command[2]);int endTime = Integer.parseInt(command[3]);int goodsId = Integer.parseInt(command[4]);int limitQuantity = Integer.parseInt(command[5]);System.out.println(main.addActivity(startTime, endTime, goodsId, limitQuantity));} else if("buy".equals(command[1])) {int time = Integer.parseInt(command[0]);int activityId = Integer.parseInt(command[2]);int quantity = Integer.parseInt(command[3]);System.out.println(main.buyGoods(time, activityId, quantity));} else if("list".equals(command[1])){int time = Integer.parseInt(command[0]);List<Activity> list = main.getActivityList(time);for (Activity activity : list) {System.out.print(activity.id+" ");}System.out.println();}}}}class Good {public int id;public int renQi;public int kuCun;
}class Activity {public int id;public int startTime;public int endTime;public int goodsId;public int limitQuantity;public int sellTime;
}