卡勒沃夫之弱水路三千1

package 搜索;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;


public class 卡勒沃夫之弱水路三千1 {
static int N;
static String[] topo = new String[10000];
static int t = 0;
static Map<String, ArrayList<String>> map = new HashMap<String, ArrayList<String>>();
static Map<String, Integer> c = new HashMap<String, Integer>();


static boolean dfs(String n) {
c.put(n, -1);
List<String> ls = map.get(n);
if (ls != null)
for (String key : ls) {
if (c.get(key) != null && c.get(key) == -1)
return false;
else if (c.get(key) == null && !dfs(key))
return false;
}
c.put(n, 1);
topo[t++] = n;


return true;
}


public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
N = sc.nextInt();
while (N-- != 0) {
int k = sc.nextInt();
for (int i = 0; i < k; i++) {
String s1 = sc.next();
String s2 = sc.next();
if (map.get(s1) != null) {
map.get(s1).add(s2);
} else {
ArrayList<String> al = new ArrayList<String>();
al.add(s2);
map.put(s1, al);
}
}
Set<String> set = map.keySet();
for (String key : set) {
if (c.get(key) == null) {
if (!dfs(key))
return;
}
}
for (int i = t - 1; i >= 0; i--)
System.out.print(topo[i] + " ");
System.out.println();
map.clear();
c.clear();
t = 0;
}


}
}