题目

给你一个数组 orders，表示客户在餐厅中完成的订单，确切地说， orders[i]=[customerNamei,tableNumberi,foodItemi] ，其中 customerNamei 是客户的姓名，tableNumberi 是客户所在餐桌的桌号，而 foodItemi 是客户点的餐品名称。

请你返回该餐厅的 点菜展示表 。在这张表中，表中第一行为标题，其第一列为餐桌桌号 “Table” ，后面每一列都是按字母顺序排列的餐品名称。接下来每一行中的项则表示每张餐桌订购的相应餐品数量，第一列应当填对应的桌号，后面依次填写下单的餐品数量。

注意：客户姓名不是点菜展示表的一部分。此外，表中的数据行应该按餐桌桌号升序排列。

示例 1：

输入：orders = [["David","3","Ceviche"],["Corina","10","Beef Burrito"],["David","3","Fried Chicken"],["Carla","5","Water"],["Carla","5","Ceviche"],["Rous","3","Ceviche"]]
输出：[["Table","Beef Burrito","Ceviche","Fried Chicken","Water"],["3","0","2","1","0"],["5","0","1","0","1"],["10","1","0","0","0"]]
解释：
点菜展示表如下所示：
Table,Beef Burrito,Ceviche,Fried Chicken,Water
3    ,0           ,2      ,1            ,0
5    ,0           ,1      ,0            ,1
10   ,1           ,0      ,0            ,0
对于餐桌 3：David 点了 "Ceviche" 和 "Fried Chicken"，而 Rous 点了 "Ceviche"
而餐桌 5：Carla 点了 "Water" 和 "Ceviche"
餐桌 10：Corina 点了 "Beef Burrito"

示例 2：

输入：orders = [["James","12","Fried Chicken"],["Ratesh","12","Fried Chicken"],["Amadeus","12","Fried Chicken"],["Adam","1","Canadian Waffles"],["Brianna","1","Canadian Waffles"]]
输出：[["Table","Canadian Waffles","Fried Chicken"],["1","2","0"],["12","0","3"]]
解释：
对于餐桌 1：Adam 和 Brianna 都点了 "Canadian Waffles"
而餐桌 12：James, Ratesh 和 Amadeus 都点了 "Fried Chicken"

示例 3：

输入：orders = [["Laura","2","Bean Burrito"],["Jhon","2","Beef Burrito"],["Melissa","2","Soda"]]
输出：[["Table","Bean Burrito","Beef Burrito","Soda"],["2","1","1","1"]]

提示：

• 1 <= orders.length <= 5 * 10^4
• orders[i].length == 3
• 1 <= customerNamei.length, foodItemi.length <= 20
• customerNamei 和 foodItemi 由大小写英文字母及空格字符 ' ' 组成。
• tableNumberi 是 1 到 500 范围内的整数。

思路

Collections.sort

解法

class Solution {
    public List<List<String>> displayTable(List<List<String>> orders) {
        List<List<String>> res=new ArrayList<>();
        List<Integer> tableId=new ArrayList<>();
        List<String> title=new ArrayList<>();
        Map<String,Integer> dish=new HashMap<>();

        //计算标题和桌号
        for(List<String> order:orders){
            String key=order.get(1)+"_"+order.get(2);
            dish.put(key,dish.getOrDefault(key,0)+1);

            if(!tableId.contains(Integer.valueOf(order.get(1)))){
                tableId.add(Integer.valueOf(order.get(1)));
            }   

            if(!title.contains(order.get(2))){
                title.add(order.get(2));
            }          
        }
        Collections.sort(tableId);
        Collections.sort(title);
        title.add(0,"Table");

        //添加餐品数量
        res.add(title);
        for(int i=0;i<tableId.size();i++){
            String id=String.valueOf(tableId.get(i));
            List<String> display=new ArrayList<>();
            display.add(id);
            for(int j=1;j<title.size();j++){
                String key=id+"_"+title.get(j);
                if(dish.containsKey(key)){
                    display.add(String.valueOf(dish.get(key)));
                }
                else{
                    display.add("0");
                }
            }
            res.add(display);

        }
        return res;
    }
}

总结

• 分析出几种情况，然后分别对各个情况实现