//第一题 dfs import java.util.LinkedList; import java.util.Queue; import java.util.Scanner; public class test1 { public static void main(String[] args) { Scanner scan = new Scanner(System.in); int num = scan.nextInt(); Queue<Integer>[] queue = (LinkedList<Integer>[]) new LinkedList[num+1]; for (int i = 1; i <= num; i++){ queue[i] = new LinkedList<>(); } for (int i = 1; i <= num; i++){ int k = scan.nextInt(); while (k != 0){ queue[i].add(k); queue[k].add(i); k = scan.nextInt(); } } boolean[] marked = new boolean[num+1]; //维护一个标记数组 int count = 0; for (int i = 1; i <= num; i++){ if (!marked[i]) { dfs(queue, marked, i); count++; } } System.out.println(count); } public static void dfs(Queue<Integer>[] queue, boolean[] marked, int v){ marked[v] = true; for (int w : queue[v]){ if (!marked[w]) { dfs(queue, marked, w); } } } }