蓝桥杯2017国赛JAVAB组 树形显示 题解
标题:树形显示
对于分类结构可以用树形来形象地表示。比如:文件系统就是典型的例子。
树中的结点具有父子关系。我们在显示的时候,把子项向右缩进(用空格,不是tab),并添加必要的连接线,以使其层次关系更醒目。
下面的代码就是为了这个目的的,请仔细阅读源码,并填写划线部分缺少的代码。
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 = ___________________________________ ; // 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 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");
}
}
对于题目中的测试数据,输出结果:
+--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
如有平字体对齐问题,可以参见图【p1.png】
注意,只填写划线部分缺少的代码,不要抄写已有的代码或符号。
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"); } }