摘要：
想法：dfs+优化提示：得到答案后，您可以追溯到路径#include 使用namespacestd；组分maxn=10000+5；整数[maxn]；boolisp[maxn]；intcentg[maxn]；intmaxceng=0；vector＜int＞vmaxn；intdfs｛ifreturnceng[现在]；如果｛ceng[当前]=1；return1；｝ceng[现在]=dfs+1；returnceng[现在]；}intmain（）｛intn；cin˃˃n；forfate[i]=i；对于｛intt；cin˃˃t；ifisp[i]=true；对于{intx；cin˃˃x；fate[x]=i；｝｝对于{if{ceng[i]=dfs；if{maxceng=ceng[i]；vmaxn.clear（）；intnow=i；while（father[now]！
思路：
dfs+优化
Tip：
得到答案后回溯可得到路径
#include <bits/stdc++.h>
using namespace std;
const int maxn = 10000 + 5;
int father[maxn];
bool isp[maxn];
int ceng[maxn];
int maxceng = 0;
vector<int> vmaxn;
int dfs(int now) {
if (ceng[now])
return ceng[now];
if (father[now] == now) {
ceng[now] = 1;
return 1;
}
ceng[now] = dfs(father[now]) + 1;
return ceng[now];
}
int main() {
int n;
cin >> n;
for (int i = 0; i < n; i++)
father[i] = i;
for (int i = 0; i < n; i++) {
int t;
cin >> t;
if (t == 0)
isp[i] = true;
for (int j = 1; j <= t; j++) {
int x;
cin >> x;
father[x] = i;
}
}
for (int i = 0; i < n; i++) {
if (isp[i]) {
ceng[i] = dfs(i);
if (ceng[i] > maxceng) {
maxceng = ceng[i];
vmaxn.clear();
int now = i;
while (father[now] != now) {
vmaxn.push_back(now);
now = father[now];
}
vmaxn.push_back(now);
} else if (ceng[i] == maxceng) {
vector<int> vnow;
int now = i;
while (father[now] != now) {
vnow.push_back(now);
now = father[now];
}
vnow.push_back(now);
bool flag = false;
for (int k = maxceng - 1; k >= 0; k--) {
if (vnow[k] < vmaxn[k]) {
flag = true;
break;
} else if (vnow[k] > vmaxn[k]) {
flag = false;
break;
}
}
if (flag)
vmaxn = vnow;
}
}
}
cout << maxceng << endl;
bool first = true;
for (int k = maxceng - 1; k >= 0; k--) {
if (first) {
first = false;
cout << vmaxn[k];
} else
cout << " " << vmaxn[k];
}
return 0;
}