卡勒沃夫之弱水路三千

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


public class 卡勒沃夫之弱水路三千 {
static Map<String, ArrayList<String>> map = new HashMap<>();
static String[] result = new String[1000];
static int top = 0;
static HashSet<String> visited = new HashSet<>();


public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int t = sc.nextInt();
while (t-- > 0) {
int n = sc.nextInt();
for (int i = 0; i < n; i++) {
String s1 = sc.next();
String s2 = sc.next();
ArrayList<String> arrayList = map.get(s1);
if (arrayList == null) {
arrayList = new ArrayList<>();
}
arrayList.add(s2);
map.put(s1, arrayList);
}
Set<String> set = map.keySet();
for (String str : set) {
if (!visited.contains(str)) {
dfs(str);
}
}
for (int i = top - 1; i >= 0; i--) {
System.out.print(result[i] + " ");
}
System.out.println();
result = new String[1000];
top = 0;
map.clear();
visited.clear();
}


}


private static void dfs(String str) {
visited.add(str);
ArrayList<String> arrayList = map.get(str);
if (arrayList != null) {
for (String s : arrayList) {
if (!visited.contains(s)) {
dfs(s);
}
}
}
result[top++] = str;
}
}