The third question of Java Group B of the 8th Blue Bridge Cup National Championship

Title: Tree Display


The classification structure can be represented visually by a tree. For example: file system is a typical example.


Nodes in the tree have a parent-child relationship. When we display it, we indent the subitems to the right (with spaces, not tabs) and add the necessary connecting lines to make the hierarchy more visible.


The following code is for this purpose, please read the source code carefully and fill in the missing code in the underlined part.




import java.util.*;


class MyTree
{
private Map<String, List<String>>  map_ch = new HashMap<String, List<String>>();
private Map<String,String> map_pa = new HashMap<String,String>();

public void add(String parent, String child)
{
map_pa.put(child, parent);

List<String> lst = map_ch.get(parent);
if(lst==null){
lst = new ArrayList<String>();
map_ch.put(parent, lst);
}
lst.add(child);
}

public String get_parent(String me){
return map_pa.get(me);
}

public List<String> get_child(String me){
return map_ch.get(me);
}

private String space(int n)
{
String s = "";
for(int i=0; i<n; i++) s += ' ';
return s;
}

private boolean last_child(String x){
String pa = map_pa.get(x);
if(pa==null) return true;

List<String> lst = map_ch.get(pa);
return lst.get(lst.size()-1).equals(x);
}

public void show(String x){

String s = "+--" + x;

String pa = x;
while(true){
pa = map_pa.get (pa);
if(pa==null) break;
s = ___________________________________ ; // fill in the blanks
}

System.out.println(s);
}

public void dfs(String x){
show(x);

List<String> lst = map_ch.get(x);
if(lst==null) return;

for(String it: lst){
dfs(it);
}
}
}


public class TreeView
{
public static void main(String[] args)
{
MyTree tree = new MyTree();
tree.add("root", "dog");
tree.add("root", "cat");
tree.add("root", "duck");
tree.add("dog", "AAdog");
tree.add("dog", "BBdog");
tree.add("dog", "CCdog");
tree.add("AAdog", "AAdog01");
tree.add("AAdog", "AAdog02");
tree.add("cat", "XXcat");
tree.add("cat", "YYcat");
tree.add("XXcat","XXcat-oo");
tree.add("XXcat","XXcat-qq");
tree.add("XXcat-qq", "XXcat-qq-hahah");
tree.add("duck", "TTduck");
tree.add("TTduck", "TTduck-001");
tree.add("TTduck", "TTduck-002");
tree.add("TTduck", "TTduck-003");
tree.add("YYcat","YYcat.hello");
tree.add("YYcat","YYcat.yes");
tree.add("YYcat","YYcat.me");

tree.dfs("root");
}
}


For the test data in the question, output the result:
+--root
     +--dog
     | +--AAdog
     | | +--AAdog01
     | | +--AAdog02
     | +--BBdog
     | +--CCdog
     +-- cat
     | +--XXcat
     | | +--XXcat-oo
     | | +--XXcat-qq
     | | +--XXcat-qq-hahah
     | +--YYcat
     | +--YYcat.hello
     | +--YYcat. yes
     | +--YYcat.me
     +--duck
          +--TTduck
               +--TTduck-001
               +--TTduck-002
               +--TTduck-003
  
If there is a problem with the alignment of the flat font, please refer to the figure [p1.png]


Note that only fill in the missing code in the underlined part, and do not copy the existing code or symbols.