蓝桥杯2017国赛JAVAB组 树形显示 题解

package 树形显示;

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 = !last_child(pa) ? "|"+space(5)+s : space(5)+s; // 填空
        }
        
        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 Main
{
    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");
    }
}