Java递归算法实例

 public static void main(String[] args) {
        Map<String,Object> map = new HashMap<>();
        map.put("id",0);
        map.put("name","a");
        map.put("pid",55);
        Map<String,Object> map1 = new HashMap<>();
        map1.put("id",1);
        map1.put("name","aa");
        map1.put("pid",0);
        Map<String,Object> map2 = new HashMap<>();
        map2.put("id",2);
        map2.put("name","bb");
        map2.put("pid",0);
        Map<String,Object> map3 = new HashMap<>();
        map3.put("id",3);
        map3.put("name","aaa");
        map3.put("pid",1);
        Map<String,Object> map4 = new HashMap<>();
        map4.put("id",4);
        map4.put("name","bbb");
        map4.put("pid",2);
        List<Map<String,Object>> list = new ArrayList<>();
        list.add(map);
        list.add(map1);
        list.add(map2);
        list.add(map3);
        list.add(map4);

        List<Map<String, Object>> dg = dg(55, list);
        System.out.println(dg);

    }

    public static List<Map<String,Object>> dg(Integer id, List<Map<String,Object>> mapList){
        List<Map<String,Object>> childList = new ArrayList<>();
        for (Map<String,Object> map : mapList) {
            System.out.println(map.get("pid"));
            if((int)map.get("pid")== id){
                childList.add(map);
            }
        }

        for (Map<String,Object> map : childList){
            List<Map<String, Object>> childList1 = dg((Integer) map.get("id"), mapList);
            map.put("child",childList1);
        }
        if (childList.size()==0){
            return null;
        }

        return childList;
    }

执行结果：