Submission #586793

#	Time	Username	Problem	Language	Result	Execution time	Memory
586793		blue	Valley (BOI19_valley)	C++17	100 / 100	203 ms	36640 KiB

valley

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

using vi = vector<int>;
using vvi = vector<vi>;
using ll = long long;
using vll = vector<ll>;
#define sz(x) int(x.size())

const int mx = 100'001;
const int lg = 17;
const ll inf = 1'000'000'000'000'000'000LL;

int N, S, Q, E;

vi A(1+mx), B(1+mx);
vll W(1+mx);
vi edgeind[1+mx];

vll nearshop(1+mx, inf); //distance to closest shop within subtree


vi parent(1+mx, 0);
vi paredge(1+mx, 0);
vll distE(1+mx, 0);
vi depth(1+mx, 0);

vi edgelower(1+mx, 0);

int dfsct = 0;
vi dfsind(1+mx, 0);
vi subtree(1+mx, 1);

void dfs(int u, int p)
{
	dfsct++;
	dfsind[u] = dfsct;

	for(int e : edgeind[u])
	{
		int v = A[e] + B[e] - u;
		ll w = W[e];

		if(v == p)
			continue;

		parent[v] = u;
		paredge[v] = e;
		edgelower[e] = v;

		distE[v] = distE[u] + w;
		depth[v] = depth[u] + 1;

		dfs(v, u);

		nearshop[u] = min(nearshop[u], nearshop[v] + w);

		subtree[u] += subtree[v];
	}
}

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

	cin >> N >> S >> Q >> E;

	for(int e = 1; e <= N-1; e++)
	{
		cin >> A[e] >> B[e] >> W[e];
		edgeind[A[e]].push_back(e);
		edgeind[B[e]].push_back(e);
	}

	for(int x = 1; x <= S; x++)
	{
		int u;
		cin >> u;
		nearshop[u] = 0;
	}

	dfs(E, 0);

	parent[E] = E;

	ll lft[1+N][1+lg];
	int anc[1+N][1+lg];
	for(int i = 1; i <= N; i++)
	{
		lft[i][0] = nearshop[i] - distE[i];
		anc[i][0] = parent[i];
	}

	for(int e = 1; e <= lg; e++)
	{
		for(int i = 1; i <= N; i++)
		{
			anc[i][e] = anc[ anc[i][e-1] ][e-1];
			lft[i][e] = min(lft[i][e-1], lft[ anc[i][e-1] ][e-1]);
		}
	}

	// cerr << "nearshop = ";
	// for(int i = 1; i <= N; i++)
	// 	cerr << nearshop[i] << ' ';
	// cerr << '\n';


	for(int q = 1; q <= Q; q++)
	{
		int I, R;
		cin >> I >> R;

		bool escape;
		int A;

		if(R == E)
			escape = 1;
		else
		{
			A = edgelower[I];
			if(dfsind[A] <= dfsind[R] && dfsind[R] < dfsind[A] + subtree[A])
				escape = 0;
			else
				escape = 1;
		}

		if(escape)
			cout << "escaped\n";
		else
		{
			if(nearshop[A] >= inf)
				cout << "oo\n";
			else
			{
				// cerr << "A = " << A << '\n';
				ll res = inf;
				int u = R;
				for(int e = lg; e >= 0; e--)
				{
					if((1 << e) & (depth[u] - depth[A] + 1))
					{
						// cerr << "jump by " << (1<<e) << '\n';
						res = min(res, distE[R] + lft[u][e]);
						u = anc[u][e];
					}
				}

				cout << res << '\n';
			}
		}
	}
}

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