objects 的扁平树同时保留父亲和 child

Question

我有一个 class 员工，其树结构为属性 team

public class Employee {

    private String name;
    private List<Employee> team;
}

使用 Java lambda 我需要将这棵树平展到同一级别的列表中，同时将 Employee class 转换为以下 ConvertedEmployee，同时将名称存储在专用的 lead 和 subordinates 中特性。因此，ConvertedEmployee 在某种意义上是一个保持 parent 和 children 的节点。我需要一份清单。

    public class ConvertedEmployee {

    private String name;
    private String lead;
    private List<String> subordinatesNames;
}

所以最终结果应该是List<ConvertedEmployee>

我想在这里使用递归。

但是我只能把树弄平，不能重建它的parents。

编辑：输入是 Employee object 的实例，它基本上在 team

中有一棵树

Answer 1

一种非递归解决方案，使用流的串联，然后过滤掉没有设置 lead 字段的“重复”条目：

public static List<ConvertedEmployee> convert(List<Employee> staff) {
    return staff
        .stream()
        .flatMap(e -> Stream.concat(
            // subordinates of current employee
            e.getTeam()
             .stream()
             .map(sub -> new ConvertedEmployee(
                 sub.getName(), e.getName(),
                 sub.getTeam().stream().map(Employee::getName).collect(Collectors.toList())
             )),
            // current employee by themself
            Stream.of(new ConvertedEmployee(
                 e.getName(), null,
                 e.getTeam().stream().map(Employee::getName).collect(Collectors.toList())
            ))
        ))
        .collect(Collectors.collectingAndThen(
            Collectors.toMap(
                ConvertedEmployee::getName,
                c -> c,
                (e1, e2) -> e1.getLead() != null ? e1 : e2.getLead() != null ? e2 : e1,
                LinkedHashMap::new
            ),
            map -> new ArrayList<>(map.values())
        ));
}

测试以下设置：

Employee intern = new Employee("intern", Collections.emptyList());
Employee junior = new Employee("junior", Collections.emptyList());
Employee middleDev = new Employee("mid", Arrays.asList(junior));
Employee devOps = new Employee("devOps", Collections.emptyList());
Employee teamLead = new Employee("teamLead", Arrays.asList(intern, middleDev));
Employee pm = new Employee("mgr", Arrays.asList(teamLead, devOps));

List<Employee> staff = Arrays.asList(intern, junior, middleDev, devOps, teamLead, pm);

convert(staff).forEach(System.out::println);

输出：

ConvertedEmployee(name=intern, lead=teamLead, subordinatesNames=[])
ConvertedEmployee(name=junior, lead=mid, subordinatesNames=[])
ConvertedEmployee(name=mid, lead=teamLead, subordinatesNames=[junior])
ConvertedEmployee(name=devOps, lead=mgr, subordinatesNames=[])
ConvertedEmployee(name=teamLead, lead=mgr, subordinatesNames=[intern, mid])
ConvertedEmployee(name=mgr, lead=null, subordinatesNames=[teamLead, devOps])

objects 的扁平树同时保留父亲和 child

Flat tree of objects while keeping father and child

java

tree

recursion

java-stream