Submission #1307422

#	Time	Username	Problem	Language	Result	Execution time	Memory
1307422		pvpro	From Hacks to Snitches (BOI21_watchmen)	C++20	15 / 100	6102 ms	319412 KiB

watchmen

#ifndef LOCAL
#pragma GCC Optimize("O3,Ofast,unroll-loops")
#pragma GCC Target("bmi,bmi2,avx,avx2")
#endif
#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ld = long double;

#define f first 
#define s second 
#define mp make_pair 
#define pb push_back
#define pii pair<int, int>
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin() (x).rend()
#ifndef LOCAL
#define endl "\n"
#endif

mt19937 rnd(11);

void solve() {
    int n, m;
    cin >> n >> m;
    vector<vector<pii>> graph(n);
    map<pii, int> E;
    for (int i = 0; i < m; ++i) {
        int a, b;
        cin >> a >> b;
        --a; --b;
        E[mp(a, b)] = i;
        E[mp(b, a)] = i;
        graph[a].pb(mp(b, i));
        graph[b].pb(mp(a, i));
    }
    int k;
    cin >> k;
    vector<pii> bad(n, mp(0, 0));
    vector<pii> badE(m, mp(0, 0));
    int L = 0;
    for (int i = 0; i < k; ++i) {
        int sz;
        cin >> sz;
        L = max(L, sz);
        assert(sz > 2);
        vector<int> v(sz);
        for (auto &x : v) {
            cin >> x;
            --x;
        }
        for (int j = 0; j < sz; ++j) {
            bad[v[j]] = mp(sz, j);
            badE[E[mp(v[j], v[(j + 1) % v.size()])]] = mp(sz, j);
        }
    }
    auto ok = [&](int v, int t) {
        return (bad[v].f == 0 || (t % bad[v].f != bad[v].s));
    };
    vector<int> d(n, 1e9);
    vector<bitset<150>> marked(n);
    marked[0][0] = 1;
    d[0] = 0;
    queue<pii> q;
    q.push(mp(0, 0));
    while (!q.empty()) {
        auto p = q.front();
        q.pop();
        int v = p.f;
        int t = p.s;
        if (t + 1 < d[v] + L && ok(v, t + 1) && !marked[v][t + 1 - d[v]]) {
            q.push(mp(v, t + 1));
        }
        for (auto &u : graph[v]) {
            if (ok(u.f, t + 1) && (badE[u.s].f == 0 || (t % badE[u.s].f != badE[u.s].s))) {
                if (d[u.f] == 1e9) {
                    d[u.f] = t + 1;
                    marked[u.f][0] = 1;
                    q.push(mp(u.f, t + 1));
                } else if (d[u.f] + L > t + 1 && !marked[u.f][t + 1 - d[u.f]]) {
                    marked[u.f][t + 1 - d[u.f]] = 1;
                    q.push(mp(u.f, t + 1));
                }
            }
        }
    }
    if (d.back() == 1e9) {
        cout << "impossible" << endl;
    } else {
        cout << d.back() << endl;
    }
}

signed main() {
    #ifdef LOCAL
        freopen("in.txt", "r", stdin);
        freopen("out.txt", "w", stdout);
    #else
        ios::sync_with_stdio(false);
        cin.tie(0);
    #endif
    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }
}

• Subtask 1: 5 / 5
• Subtask 2: 10 / 10
• Subtask 3: 0 / 10
• Subtask 4: 0 / 10
• Subtask 5: 0 / 25
• Subtask 6: 0 / 20
• Subtask 7: 0 / 20