如何从列表中计算玩家的等级 [英] How to calculate the rank of a player from a list

问题描述

说我有以下简单的数据结构。

Say I have following simple data structure.

public class Player {
    private Long id;
    private String name;
    private Integer scores;

    //getter setter
}

到目前为止一切顺利。现在的问题是，我如何获得球员排名？
我有另一种排名数据结构，即 -

So far so good. Now question is , how do I get what's a players rank? I have another data structure for ranking, that is-

public class Ranking {
    private Integer score;
    private Integer rank;

    //getter/setter

}

所以我有一个播放器列表，我想计算一个排名列表，我想使用java8 stream api。

So I have a list of player and i want to compute a list of ranking and I would like to use java8 stream api.

我有一个名为<$ c的服务$ c> PlayerService 如下：

public class PlayerService {

    @Autowired
    private PlayerRepository playerRepository;


    public List<Ranking> findAllRanking(Long limit) {
        List<Player> players = playerRepository.findAll();

       // calculation 

        return null;
    }

计算很简单，得分最高的人排名最高。

The calculation is simple, whoever has most score has most ranking.

如果我有 5,7,8,9,3 分数，那么排名将是

If I have 5,7,8,9,3 scores then ranking would be

rank score 
  1   9
  2   8 
  3   7
  4   5
  5   3

任何帮助将不胜感激。

Any help would be appreciated.

推荐答案

试试这个：

     List<Player> players = new ArrayList<Player>() {{
        add(new Player(1L, "a", 5));
        add(new Player(2L, "b", 7));
        add(new Player(3L, "c", 8));
        add(new Player(4L, "d", 9));
        add(new Player(5L, "e", 3));
        add(new Player(6L, "f", 8));
     }};
     int[] score = {Integer.MIN_VALUE};
     int[] no = {0};
     int[] rank = {0};
     List<Ranking> ranking = players.stream()
         .sorted((a, b) -> b.getScores() - a.getScores())
         .map(p -> {
             ++no[0];
             if (score[0] != p.getScores()) rank[0] = no[0];
             return new Ranking(rank[0], score[0] = p.getScores());
         })
         // .distinct() // if you want to remove duplicate rankings.
         .collect(Collectors.toList());
     System.out.println(ranking);
    // result:
    // rank=1, score=9
    // rank=2, score=8
    // rank=2, score=8
    // rank=4, score=7
    // rank=5, score=5
    // rank=6, score=3

变量得分，否和 rank 是 .map（）中lambda函数中的自由变量。所以不能重新分配它们。如果它们的类型是 int 而不是 int [] ，则无法编译代码。

The variables score, no and rank are free variables in the lambda function in .map(). So they must not be reassigned. If their types are int instead of int[], you cannot compile the code.

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