Submission #997155

#	Time	Username	Problem	Language	Result	Execution time	Memory
997155		goats_9	Valley (BOI19_valley)	C++17	100 / 100	265 ms	77392 KiB

valley

/* Author: goats_9 */

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

using ll = long long;
const ll INF = 1e16;
const int LOG = 18;

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	int n, s, q, e;
	cin >> n >> s >> q >> e;
	vector<array<ll, 3>> edges(n);
	vector<ll> store(n+1, INF), depth(n+1), in(n + 1), out(n + 1);
	vector<vector<ll>> par(n+1, vector<ll> (LOG)), parlen(n+1, vector<ll> (LOG)), parcost(n+1, vector<ll> (LOG, INF));
	vector<vector<array<ll, 2>>> adj(n+1, vector<array<ll, 2>>());
	for (int i = 1; i < n; i++) {
		int u, v, w;
		cin >> u >> v >> w;
		edges[i] = {u, v, w}; 
		adj[u].push_back({v, w});
		adj[v].push_back({u, w});
	}
	while (s--) {
		int x;
		cin >> x;
		store[x] = 0;
	}
	int cnt = 0;
	function<void(int, int)> dfs = [&] (int u, int p) {
		in[u] = cnt++;
		for (auto &[v, w] : adj[u]) {
			if (v == p) continue;
			depth[v] = depth[u] + 1;
			dfs(v, u);
			store[u] = min(store[u], store[v] + w);
		}
		out[u] = cnt++;
	};
	dfs(e, 0);
	function<void(int, int, ll)> dfs2 = [&] (int u, int p, ll w) {
		par[u][0] = p;
		parlen[u][0] = w;
		for (int i = 1; i < LOG; i++) {
			par[u][i] = par[par[u][i - 1]][i - 1];
			parlen[u][i] = parlen[u][i - 1] + parlen[par[u][i - 1]][i - 1];
		}
		parcost[u][0] = min(store[u], w + store[p]);
		for (int i = 1; i < LOG; i++) {
			parcost[u][i] = min(parcost[u][i - 1], parlen[u][i - 1] + parcost[par[u][i - 1]][i - 1]);
		}
		for (auto [v, w1] : adj[u]) {
			if (v == p) continue;
			dfs2(v, u, w1);
		}
	};
	dfs2(e, 0, 0);
	while (q--) {
		int i, r;
		cin >> i >> r;
		auto [u, v, w] = edges[i];
		if (depth[u] > depth[v]) swap(u, v);
		bool fl = (in[v] <= in[r]) && (out[r] <= out[v]);
		if (!fl) {
			cout << "escaped\n";
			continue;
		}
		ll ans = store[r];
		ll psm = 0;
		for (int j = LOG - 1; j >= 0; j--) {
			if (depth[par[r][j]] > depth[v]) {
				ans = min(ans, psm + parcost[r][j]);
				psm += parlen[r][j];
				r = par[r][j];
			}
		}
		if (r != v) ans = min(ans, psm + parcost[r][0]);
		if (ans == INF) cout << "oo\n";
		else cout << ans << '\n';
	}
	return 0;
}

• Subtask 1: 9 / 9
• Subtask 2: 27 / 27
• Subtask 3: 23 / 23
• Subtask 4: 41 / 41