java 如何用递归的方式实现目标

Question

我有一组部门，其中有一级部门、二级部门、三级部门、四级部门，每个部门有id、parentid、name三个属性，id是部门的序号，parentid是上级部门的id，我需要找到某个部门的所有上级部门组成一个部门全称，比如：一级部门/二级部门/三级部门/四级部门，这样的部门全称。需要用递归的方式实现，需要怎么做

Answer 1

递归，循环都可以完成，我帮你写一个

package io.springcloud.test;

import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.stream.Collectors;

class Department {
    private Integer id;
    private String name;
    private Integer parentid;

    public Department(Integer id, String name, Integer parentid) {
        super();
        this.id = id;
        this.name = name;
        this.parentid = parentid;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getParentid() {
        return parentid;
    }

    public void setParentid(Integer parentid) {
        this.parentid = parentid;
    }
}

public class MainTest {

    public static Map<Integer, Department> DATA = new HashMap<>();

    static {
        DATA.put(1, new Department(1, "部门1", null));
        DATA.put(2, new Department(2, "部门2", 1));
        DATA.put(3, new Department(3, "部门3", 2));
        DATA.put(4, new Department(4, "部门4", 3));
        DATA.put(5, new Department(5, "部门5", null));
        DATA.put(6, new Department(6, "部门6", 1));
        DATA.put(7, new Department(7, "部门7", 5));
    }

    public static void main(String[] args) throws Exception {
        
        MainTest mainTest = new MainTest();
        
        String result = mainTest.list(3, new LinkedList<>()).stream().map(Department::getName).collect(Collectors.joining("/"));
        
        System.out.println(result);  // 部门1/部门2/部门3

    }

    /**
     * 根据ID查询数据
     * @param id
     * @return
     */
    public Department findById(Integer id) {
        return DATA.get(id);
    };

    /**
     * 根据ID查询所有父级部门链
     * @param id
     * @param result
     * @return
     */
    public LinkedList<Department> list(Integer id, LinkedList<Department> result) {
        
        if (id == null) {
            return result;
        }

        Department department = findById(id);

        result.addFirst(department);

        return list(department.getParentid(), result);
    }
}