Submission #500681

#	Time	Username	Problem	Language	Result	Execution time	Memory
500681		blue	Firefighting (NOI20_firefighting)	C++17	14 / 100	3070 ms	1048580 KiB

Firefighting

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

using ll = long long;
using vll = vector<ll>;
using vvll = vector<vll>;
using vi = vector<int>;

const ll INF = 1'000'000'000'000'000'000LL;

int main()
{
    int N, K;
    cin >> N >> K;

    vvll dist(1+N, vll(1+N, INF));
    // for(int i = 1; i <= N; i++) dist[i][i] = 0;

    vvll has_edge(1+N, vll(1+N, 0));

    // vvll edge(1+N, vll(1+N, 0));

    vector< pair<int, ll> > edge[1+N];

    for(int e = 1; e <= N-1; e++)
    {
        int a, b, d;
        cin >> a >> b >> d;
        has_edge[a][b] = has_edge[b][a] = 1;
        // dist[a][b] = dist[b][a] = d;
        // edge[a][b] = edge[b][a] = 1;

        edge[a].push_back({b, d});
        edge[b].push_back({a, d});
    }

    for(int i = 1; i <= N; i++)
    {
        queue<int> tbv;
        tbv.push(i);
        dist[i][i] = 0;
        while(!tbv.empty())
        {
            int u = tbv.front();
            tbv.pop();

            for(auto q: edge[u])
            {
                int v = q.first;
                ll w = q.second;

                if(dist[i][v] < INF) continue;

                dist[i][v] = dist[i][u] + w;
                tbv.push(v);
            }
        }
    }

    // for(int k = 1; k <= N; k++)
    //     for(int i = 1; i <= N; i++)
    //         for(int j = 1; j <= N; j++)
    //             dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);

    vi par(1+N, -1);
    for(int i = 2; i <= N; i++)
    {
        for(int j = 1; j <= N; j++)
        {
            if(j == i) continue;
            if(dist[1][i] == dist[1][j] + dist[j][i] && has_edge[i][j] == 1)
            {
                par[i] = j;
                break;
            }
        }
    }

    if(N >= 100) while(1);

    vector<pair<ll, int> > V;
    for(int i = 1; i <= N; i++) V.push_back({dist[1][i], i});

    sort(V.begin(), V.end());

    vi res;

    reverse(V.begin(), V.end());

    vi covered(1+N, 0);

    for(auto q: V)
    {
        int u = q.second;

        if(covered[u]) continue;

        int v = u;
        while(v != 1 && dist[par[v]][u] <= K) v = par[v];

        res.push_back(v);

        for(int i = 1; i <= N; i++)
            covered[i] |= (dist[v][i] <= K);
    }

    cout << int(res.size()) << '\n';
    for(int r: res) cout << r << ' ';
    cout << '\n';
}

• Subtask 1: 0 / 3
• Subtask 2: 5 / 5
• Subtask 3: 9 / 9
• Subtask 4: 0 / 19
• Subtask 5: 0 / 26
• Subtask 6: 0 / 38