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| #include <cctype>
#include <cstdio>
#include <algorithm>
#include <iostream>
#include <vector>
#include <cstring>
#include <climits>
#include <queue>
#include <ctime>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/priority_queue.hpp>
using namespace std;
const int iol = 1024 * 1024;
char iobuf[iol], *ioh, *iot, ioc;
inline char read() {
if(ioh == iot) {
iot = (ioh = iobuf) + fread(iobuf, 1, iol, stdin);
if(ioh == iot) return -1;
}
return *ioh++;
}
template<class T>
inline void read(T& x) {
for(ioc = read(); !isdigit(ioc); ioc = read());
x = 0;
for(; isdigit(ioc); ioc = read())
x = (x << 1) + (x << 3) + (ioc ^ '0');
}
const int MAXN = 5000011;
struct Node {
int v;
long long w;
Node() {}
Node(int v, long long w) : v(v), w(w) {}
inline bool operator < (const Node &n) const {
return w > n.w;
}
};
vector<Node> edge[MAXN];
inline void addEdge(int u, int v, long long w) {
edge[u].push_back(Node(v, w));
edge[v].push_back(Node(u, 0));
}
int n, m;
bool vis[MAXN];
long long dis1[MAXN], disn[MAXN];
const long long INF = LONG_LONG_MAX >> 1;
typedef __gnu_pbds::priority_queue<Node> Heap;
Heap::point_iterator id[MAXN];
inline void dijkstra(int s, long long *dis) {
fill(dis + 1, dis + n + m + 1, INF);
memset(vis, 0, sizeof(bool) * (n + m + 1));
memset(id, 0, sizeof(id));
dis[s] = 0;
Heap q;
id[s] = q.push(Node(s, 0));
while (!q.empty()) {
register int now = q.top().v;
q.pop();
if (vis[now]) continue;
vis[now] = 1;
for (int i = 0; i < edge[now].size(); i++) {
Node *x = &edge[now][i];
if (x->w + dis[now] < dis[x->v]) {
dis[x->v] = x->w + dis[now];
if (id[x->v] != NULL) q.modify(id[x->v], Node(x->v, dis[x->v]));
else id[x->v] = q.push(Node(x->v, dis[x->v]));
}
}
}
}
int main() {
#ifndef ONLINE_JUDGE
freopen("farm.in", "r", stdin);
#endif
read(n), read(m);
for (int i = 1, w, ni; i <= m; i++) {
read(w), read(ni);
for (int j = 0, v; j < ni; j++) read(v), addEdge(v, n + i, w);
}
dijkstra(1, dis1);
dijkstra(n, disn);
long long tmp = INF;
for (int i = 1; i <= n; i++)
tmp = min(tmp, max(dis1[i], disn[i]));
if (tmp == INF) cout << "impossible", exit(0);
cout << tmp << "\n";
for (int i = 1; i <= n; i++)
if (max(dis1[i], disn[i]) == tmp)
cout << i << " ";
return 0;
}
|
