Submission #670373

#	Time	Username	Problem	Language	Result	Execution time	Memory
670373		finn__	Commuter Pass (JOI18_commuter_pass)	C++17	100 / 100	408 ms	24348 KiB

commuter_pass

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

size_t n, m;
vector<vector<pair<unsigned, int64_t>>> g;

void dijkstra(unsigned s, vector<int64_t> &dis, vector<vector<unsigned>> *pre = 0)
{
    priority_queue<pair<int64_t, unsigned>, vector<pair<int64_t, unsigned>>, greater<pair<int64_t, unsigned>>> q;
    q.push({0, s});
    dis[s] = 0;

    while (!q.empty())
    {
        auto const [z, u] = q.top();
        q.pop();

        if (dis[u] != z)
            continue;

        for (auto const &[v, w] : g[u])
        {
            if (z + w < dis[v])
            {
                dis[v] = z + w;
                q.push({z + w, v});
                if (pre)
                {
                    (*pre)[v].clear();
                    (*pre)[v].push_back(u);
                }
            }
            else if (z + w == dis[v] && pre)
            {
                (*pre)[v].push_back(u);
            }
        }
    }
}

int64_t min_cost(
    unsigned s, unsigned t, unsigned x, unsigned y,
    vector<int64_t> const &s_dis, vector<vector<unsigned>> const &s_pre,
    vector<int64_t> const &x_dis, vector<int64_t> const &y_dis)
{
    vector<int64_t> min_y_dis(n);
    for (unsigned u = 0; u < n; u++)
        min_y_dis[u] = y_dis[u];
    vector<bool> vis(n, 0);
    vis[t] = 1;

    int64_t min_total = INT64_MAX;

    priority_queue<pair<int64_t, unsigned>, vector<pair<int64_t, unsigned>>, greater<pair<int64_t, unsigned>>> q;
    q.push({min_y_dis[t], t});

    while (!q.empty())
    {
        auto const [z, u] = q.top();
        q.pop();

        if (z != min_y_dis[u])
            continue;

        min_total = min(min_total, min_y_dis[u] + x_dis[u]);

        for (unsigned v : s_pre[u])
        {
            if (min_y_dis[u] < min_y_dis[v])
            {
                min_y_dis[v] = min_y_dis[u];
                q.push({min_y_dis[v], v});
            }
            else if (!vis[v])
            {
                q.push({min_y_dis[v], v});
                vis[v] = 1;
            }
        }
    }

    return min_total;
}

int main()
{
    cin >> n >> m;
    unsigned s, t, x, y;
    cin >> s >> t >> x >> y;
    s--, t--, x--, y--;

    g = vector<vector<pair<unsigned, int64_t>>>(n);

    for (size_t i = 0; i < m; i++)
    {
        unsigned u, v;
        int64_t w;
        cin >> u >> v >> w;
        g[u - 1].push_back({v - 1, w});
        g[v - 1].push_back({u - 1, w});
    }

    vector<int64_t> x_dis(n, INT64_MAX), y_dis(n, INT64_MAX);
    dijkstra(x, x_dis);
    dijkstra(y, y_dis);
    vector<int64_t> s_dis(n, INT64_MAX);
    vector<vector<unsigned>> s_pre(n);
    dijkstra(s, s_dis, &s_pre);

    cout << min(x_dis[y], min(min_cost(s, t, x, y, s_dis, s_pre, x_dis, y_dis),
                              min_cost(s, t, y, x, s_dis, s_pre, y_dis, x_dis)))
         << '\n';
}

• Subtask 1: 16 / 16
• Subtask 2: 15 / 15
• Subtask 3: 24 / 24
• Subtask 4: 45 / 45