Submission #938453

#	Time	Username	Problem	Language	Result	Execution time	Memory
938453		Gromp15	From Hacks to Snitches (BOI21_watchmen)	C++17	0 / 100	1047 ms	524288 KiB

watchmen

#include <bits/stdc++.h>
#define ll long long
#define ar array
#define db double
#define all(x) x.begin(), x.end()
#define sz(x) (int)x.size()
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define rint(l, r) uniform_int_distribution<int>(l, r)(rng)
template<typename T> bool ckmin(T &a, const T &b) { return a > b ? a = b, 1 : 0; }
template<typename T> bool ckmax(T &a, const T &b) { return a < b ? a = b, 1 : 0; }
void test_case() {
	int n, m;
	cin >> n >> m;
	vector<vector<int>> adj(n+1);
	for (int i = 0; i < m; i++) {
		int x, y;
		cin >> x >> y;
		adj[x].push_back(y);
		adj[y].push_back(x);
	}
	vector<int> size(n+1, 1), who(n+1, -1), id(n+1, -1);
	int Q; cin >> Q;
	for (int i = 0; i < Q; i++) {
		int cur; cin >> cur;
		for (int j = 0; j < cur; j++) {
			int x; cin >> x;
			size[x] = cur;
			who[x] = j;
			id[x] = i;
		}
	}
	// if size[v]
	// then, dist[v] % size[v] != who[v]
	vector<vector<int>> dist(n+1);
	for (int i = 1; i <= n; i++) {
		dist[i].resize(size[i], 1e9);
	}
	// number of nodes = N + sum(L)
	const int N = 1501; // max edge length = 1500
	vector<vector<ar<int, 3>>> queues(N);
	queues[0].push_back({1, 0, 1});
	dist[1][0] = 0;
	int max_dist = 0;
	for (int cost = 0; cost <= max_dist; cost++) {
		int use = cost % N;
		while (queues[use].size()) {
			auto [v, time, len] = queues[use].back(); queues[use].pop_back();
			if (dist[v][time] == cost) {
				for (int u : adj[v]) {
					// cost + i - 1 = who[u] (mod size[u])
					// [cost, cost + i - 1] mod size[u] != who[u]
					int res;
					if (size[v] > 1) {
						if (cost % size[v] < who[v]) {
							res = who[v] - cost % size[v];
						}
						else {
							res = who[v] + (size[v] - cost % size[v]);
						}
					}
					else res = 1e9;
					ar<int, 2> avoid{int(1e9), int(1e9)};
					// (cost + i) % size[u] == who[u]
					avoid[0] = ((who[u] - cost) % size[u] + size[u]) % size[u];
					if (id[u] == id[v] && ((who[u] + 1) % size[u] == who[v])) {
						// (cost + i - 1) = who[u] (mod size[u])
						avoid[1] = ((who[u] + 1 - cost) % size[u] + size[u]) % size[u];
					}
					if (avoid[0] > avoid[1]) swap(avoid[0], avoid[1]);
					auto add = [&](int L, int R) {
						ckmin(dist[u][(cost+L)%size[u]], cost + L);
						queues[(cost + L) % N].push_back({u, (cost + L) % size[u], R-L+1});
						ckmax(max_dist, cost + R);
					};
					int to = min(res, size[u]);
					assert(avoid[0] != 1e9);
					if (1 < avoid[0]) {
						add(1, avoid[0] - 1);
					}
					if (avoid[1] > to) {
						if (avoid[0] + 1 <= to) add(avoid[0] + 1, to);
					}
					else {
						if (avoid[0] + 1 < avoid[1]) add(avoid[0] + 1, avoid[1] - 1);
						if (avoid[1] + 1 <= to) add(avoid[1] + 1, to);
					}
					/*
					for (int i = 1; i <= to; i++) if (i != avoid[0] && i != avoid[1]) {
						if (ckmin(dist[u][(cost+i)%size[u]], cost + i)) {
							queues[(cost + i) % N].push_back({u, (cost + i) % size[u], 1});
							ckmax(max_dist, cost + i);
						}
					}
					*/
				}
			}
			if (len > 1) {
				ckmin(dist[v][(cost+1)%size[v]], cost + 1);
				queues[(cost + 1) % N].push_back({v, cost + 1, len - 1});
			}
		}
	}
	int ans = *min_element(all(dist[n]));
	if (ans == 1e9) {
		cout << "impossible\n";
		return;
	}
	cout << ans << '\n';



}
int main() {
    cin.tie(0)->sync_with_stdio(0);
    int t = 1;
//    cin >> t;
    while (t--) test_case();
}

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