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| #include <bits/stdc++.h>
using namespace std;
const int LEN = 5e3 + 50;
int N, K, P, R, tot, ans = -1, arr[LEN], head[LEN], ind[LEN], val[LEN];
queue<int> q;
struct edge {
int to_, nxt_;
} e[LEN * LEN];
void add(int u, int v) {
e[tot].to_ = v, e[tot].nxt_ = head[u];
head[u] = tot++;
}
void toposort() {
for (int i = 1; i <= P; ++i) q.emplace(arr[i]);
while (!q.empty()) {
int u = q.front();
q.pop();
if (u == K) {
ans = val[K];
return;
}
for (int i = head[u]; ~i; i = e[i].nxt_) {
int v = e[i].to_;
val[v] = max(val[v], val[u] + 1);
if (--ind[v] == 0) q.emplace(v);
}
}
}
int main() {
memset(head, -1, sizeof(head));
int u, v, s, p;
cin >> N >> K >> P;
for (int i = 1; i <= P; ++i) cin >> arr[i];
cin >> R;
for (int i = 1; i <= R; ++i) {
cin >> v >> s;
for (int j = 1; j <= s; ++j) {
cin >> u;
add(u, v);
++ind[v];
}
}
toposort();
cout << ans;
}
|