邻接链表+DFS

#include <iostream>
#include <bits/stdc++.h>
#include <vector>
using namespace std;
const int MAXn=100000+10;
int n,maxm,last;
vector<int> door[MAXn];
int judge[MAXn];
void dfs(int m,int cnt){
	if(door[m].size()==0){
		if(cnt>maxm){
			maxm=cnt;
			last=m;
		}
		return;
	}
	for(int i=0;i<door[m].size();++i){
		dfs(door[m][i],cnt+1);
	}
	
}
int main()
{
	cin>>n;
	memset(judge,0,sizeof(judge));
	for(int i=1;i<=n;++i){
		int k,t;
		cin>>k;
		for(int j=1;j<=k;++j){
			cin>>t;
			judge[t]=1;
			door[i].push_back(t);
		}
	}
	int root;
		for(int j=1;j<=n;++j){
			if(judge[j]==0){
				root=j;
				break;
			}
		}
	last=root;
	dfs(root,0);
	cout<<last;
	return 0;
}