Submission #997072

#	Time	Username	Problem	Language	Result	Execution time	Memory
997072		goats_9	Valley (BOI19_valley)	C++17	0 / 100	126 ms	69716 KiB

valley

/* Author: goats_9 */

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

using ll = long long;
const ll INF = 1e15;

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	int n, s, q, e;
	cin >> n >> s >> q >> e;
	e--;
	vector<array<ll, 3>> edges(n);
	vector<ll> store(n, INF), depth(n);
	vector<vector<ll>> par(n, vector<ll> (20, -1)), parlen(n, vector<ll> (20, INF)), parcost(n, vector<ll> (20, INF));
	vector<vector<array<int, 2>>> adj(n, vector<array<int, 2>>());
	for (int i = 1; i < n; i++) {
		int u, v, w;
		cin >> u >> v >> w;
		u--, v--;
		edges[i] = {u, v, w}; 
		adj[u].push_back({v, w});
		adj[v].push_back({u, w});
	}
	while (s--) {
		int x;
		cin >> x;
		x--;
		store[x] = 0;
	}
	function<void(int, int)> dfs = [&] (int u, int p) {
		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);
		}
		for (auto [v, w] : adj[u]) {
			if (v == p) continue;
			par[v][0] = u;
			parlen[v][0] = w;
			parcost[v][0] = min(INF, w + store[u]);
		}
	};
	dfs(e, -1);
	for (int j = 1; j < 20; j++) {
		for (int i = 0; i < n; i++) {
			int u = par[i][j - 1];
			if (u == -1) continue;
			par[i][j] = par[u][j - 1];
			parlen[i][j] = parlen[i][j - 1] + parlen[u][j - 1];
			parcost[i][j] = min(parcost[i][j - 1], parlen[i][j - 1] + parcost[u][j - 1]);
		}
	}
	while (q--) {
		int i, r;
		cin >> i >> r;
		r--;
		auto [u, v, w] = edges[i];
		if (depth[u] > depth[v]) swap(u, v);
		int d = depth[r] - depth[v];
		if (d < 0) {
			cout << "escaped\n";
			continue;
		}
		if (d == 0) {
			if (r != v) cout << "escaped\n";
			else {
				if (store[r] >= INF) cout << "oo\n";
				else cout << store[r] << '\n';
			}
			continue;
		}
		ll ans = store[r];
		ll psm = 0;
		int cu = r;
		for (int j = 0; j < 20; j++) {
			if (d&(1<<j)) {
				ans = min(ans, psm + parcost[cu][j]);
				psm += parlen[cu][j];
				cu = par[cu][j];
			}
		}
		if (ans >= INF) cout << "oo\n";
		else cout << ans << '\n';
	}
	return 0;
}

• Subtask 1: 0 / 9
• Subtask 2: 0 / 27
• Subtask 3: 0 / 23
• Subtask 4: 0 / 41