Submission #391759

#	Time	Username	Problem	Language	Result	Execution time	Memory
391759		timmyfeng	Commuter Pass (JOI18_commuter_pass)	C++17	100 / 100	594 ms	28372 KiB

commuter_pass

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

const int N = 100001;

vector<array<int, 2>> adj[N], dag[N];
int n;

void dijkstra(int s, long long *dist) {
    priority_queue<array<long long, 2>> queue;
    fill(dist, dist + n + 1, LLONG_MAX);

    queue.push({0, s});
    dist[s] = 0;

    while (!queue.empty()) {
        auto [d, u] = queue.top();
        queue.pop();
        d = -d;

        if (d > dist[u]) {
            continue;
        }

        for (auto [c, w] : adj[u]) {
            if (d + w < dist[c]) {
                dist[c] = d + w;
                queue.push({-dist[c], c});
            }
        }
    }
}

long long dist[3][N];

long long solve(int s, int t) {
    priority_queue<array<long long, 3>> queue;
    for (int i = 0; i < 3; ++i) {
        fill(dist[i], dist[i] + n + 1, LLONG_MAX);
    }

    queue.push({0, s, 0});
    dist[0][s] = 0;

    while (!queue.empty()) {
        auto [d, u, k] = queue.top();
        queue.pop();
        d = -d;

        if (d > dist[k][u]) {
            continue;
        }

        if (k < 2 && d < dist[k + 1][u]) {
            dist[k + 1][u] = d;
            queue.push(array<long long, 3>{-d, u, k + 1});
        }

        for (auto [c, w] : (k == 1 ? dag[u] : adj[u])) {
            if (d + w < dist[k][c]) {
                dist[k][c] = d + w;
                queue.push(array<long long, 3>{-dist[k][c], c, k});
            }
        }
    }

    return dist[2][t];
}

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

    int m, s, t, x, y;
    cin >> n >> m >> s >> t >> x >> y;

    while (m--) {
        int u, v, w;
        cin >> u >> v >> w;
        adj[u].push_back({v, w});
        adj[v].push_back({u, w});
    }

    dijkstra(s, dist[0]);
    dijkstra(t, dist[1]);

    for (int i = 1; i <= n; ++i) {
        for (auto [j, w] : adj[i]) {
            if (dist[0][i] + w + dist[1][j] == dist[0][t]) {
                dag[i].push_back({j, 0});
            }
        }
    }

    cout << min(solve(x, y), solve(y, x)) << "\n";
}

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