import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class StudyMap {
    public static void main(String[] args) {
        HashMap<Integer, List<OKBean>> result = new HashMap<Integer, List<OKBean>>();
        List<OKBean> testList = new ArrayList<OKBean>();
        testList.add(new OKBean(1, 0));
        testList.add(new OKBean(2, 0));
        testList.add(new OKBean(3, 0));
        testList.add(new OKBean(4, 1));
        testList.add(new OKBean(5, 1));
        testList.add(new OKBean(6, 1));
        testList.add(new OKBean(7, 2));
        testList.add(new OKBean(8, 2));
        testList.add(new OKBean(9, 2));
        testList.add(new OKBean(10, 4));
        testList.add(new OKBean(11, 4));
        testList.add(new OKBean(12, 4));
        for (OKBean okbean : testList) {
            List<OKBean> okbeans = result.get(okbean.getParentId());
            if (okbeans == null) {
                okbeans = new ArrayList<OKBean>();
                result.put(okbean.getParentId(), okbeans);
            }
            okbeans.add(okbean);
        }
        displayMap(result, 1, "");
    }

    public static void displayMap(HashMap<Integer, List<OKBean>> result,
            int startKey, String str) {
        List<OKBean> list = result.get(startKey);
        for (OKBean okBean : list) {
            System.out.println(str + okBean.getId() + ":");
            if (result.containsKey(okBean.getId())) {
                displayMap(result, okBean.getId(), str + "  ");
            }
        }
    }
}

class OKBean {
    public OKBean() {

    }

    public OKBean(int id, int parentId) {
        this.id = id;
        this.parentId = parentId;
    }

    private int id;
    private int parentId;

    public int getId() {
        return id;
    }

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

    public int getParentId() {
        return parentId;
    }

    public void setParentId(int parentId) {
        this.parentId = parentId;
    }
}