Submission #960053

#	Time	Username	Problem	Language	Result	Execution time	Memory
960053		josanneo22	From Hacks to Snitches (BOI21_watchmen)	C++17	5 / 100	1189 ms	102448 KiB

watchmen

#include <bits/stdc++.h>
using namespace std;
using i64 = long long;

#define L(i,j,k) for(int i=(j);i<=(k);++i)
#define R(i,j,k) for(int i=(j);i>=(k);--i)
#define rep(i, n) L(i, 1, n)
#define all(x) x.begin(),x.end()
#define me(x,a) memset(x,a,sizeof(x))

#include<random>
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int nax = 100005;
int N, M, K, a[nax], dis[nax][126], vis[nax][126];
int nxt[nax * 2], head[nax * 2], ver[nax * 2], tot = 0;
void add_edge(int u, int v) {
	++tot;
	ver[tot] = v;
	nxt[tot] = head[u];
	head[u] = tot;
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr); cout.tie(nullptr);
	
	/* Given a graph of N vertices and M edges
	 * We are also given K guards where the guard will petrol a -> b -> c -> d -> a -> ...
	 * Print the minimum time for which we can reach node N or print impossible
	 */
	 
	 cin >> N >> M;
	 L(i, 1, M) {
		 int u, v; cin >> u >> v;
		 add_edge(u, v);
		 add_edge(v, u);
	 }
	 int X; cin >> X;
	 cin >> K; L(i, 0, K - 1) cin >> a[i];
	 queue<pair<int,int>> Q;
	 L(i, 1, N) L(j, 0, K - 1) { vis[i][j] = false; dis[i][j] = 1E9;}
	 Q.push(make_pair(1, 0));
	 dis[1][0] = 0;
	 while (Q.size()) {
		 pair<int,int> top = Q.front(); Q.pop();
		 int u = top.first, i = top.second;
		 if (vis[u][i]) continue;
		 vis[u][i] = true;
		 int guard_position = a[(i + 1) % K], next_ind = (i + 1) % K;
		 if (guard_position != u && dis[u][next_ind] > dis[u][i]) {
			 dis[u][next_ind] = dis[u][i] + 1;
			 Q.push(make_pair(u, next_ind));
		 } 
		 for (int P = head[u]; P; P = nxt[P]) {
			 int v = ver[P];
			 if (guard_position == u && a[i] == v) continue;
			 if (guard_position == v) continue;
			 if (dis[v][next_ind] > dis[u][i] + 1) {
				 dis[v][next_ind] = dis[u][i] + 1;
				 Q.push(make_pair(v, next_ind));
			 }
		 }
	 }
	 int ans = 1E9;
	 L(i, 0, K - 1) ans = min(ans, dis[N][i]);
	 if (ans == 1E9) cout << "impossible\n";
	 else cout << ans << '\n';
}

• Subtask 1: 5 / 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