Submission #958478

#	Time	Username	Problem	Language	Result	Execution time	Memory
958478		BhavayGoyal	Olympic Bus (JOI20_ho_t4)	C++14	5 / 100	1068 ms	5892 KiB

ho_t4

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

#define int long long
#define vi vector<int>
#define vii vector<vector<int>>
#define pii pair<int, int>
#define pb push_back
#define f first
#define s second
#define endl "\n"

const int linf = 1e15;

// -------------------------------------------------- Main Code --------------------------------------------------

const int N = 201, M = 50001;
int n, m;
set<pii> g[N];
vii edges;
map<pair<int, int>, bool> isShort;

void dijkstra(int source) {
    priority_queue<pii, vector<pii>, greater<>> q;
    vi vis(n+1, 0), dis(n+1, linf), par(n+1);
    q.push({0, source});
    dis[source] = 0;
    while (!q.empty()) {
        pii f = q.top(); q.pop();
        int src = f.s;
        if (vis[src]) continue;
        vis[src] = true;

        for (auto child : g[src]) {
            int ch = child.f, wt = child.s;
            if (dis[ch] > dis[src] + wt) {
                par[ch] = src;
                isShort[{par[ch], ch}] = true;
                dis[ch] = dis[src] + wt;
                q.push({dis[ch], ch});
            }
        }
    }

    // int x = (source==1?n:1);
    // while (par[x]) {
    //     isShort[{par[x], x}] = true;
    //     x = par[x];
    // }
}

int get_dist(int s, int t) {
    vi D(n+1, linf);
    priority_queue<pii, vector<pii>, greater<pii>> pq;
    D[s] = 0;
    pq.emplace(0, s);
    while (pq.size()) {
        pii temp = pq.top(); int x = temp.f, u = temp.s;
        pq.pop();
        if (D[u] == x) {
            for (pii child : g[u]) {
                int v = child.f, wt = child.s;
                if (D[v] > x + wt) {
                    pq.emplace(D[v] = x + wt, v);
                }
            }
        }
    }
    return D[t];
}


void sol() {
    cin >> n >> m;
    vii dist(n+1, vi(n+1, linf));
    for (int i = 1; i <= n; i++) dist[i][i] = 0;

    for (int i = 1; i <= m; i++) {
        int a, b, c, d; cin >> a >> b >> c >> d;
        dist[a][b] = min(dist[a][b], c);
        g[a].insert({b, c});
        edges.pb({a, b, c, d});
    }

    dijkstra(1);
    dijkstra(n);
    
    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]);
            }
        }
    }

    int ans = min(linf, dist[1][n] + dist[n][1]);

    for (auto i : edges) {
        int a = i[0], b = i[1], c = i[2], d = i[3];
        // if (isShort[{a, b}]) {
            g[a].erase({b, c});
            g[b].insert({a, c});
            ans = min(ans, get_dist(1, n) + get_dist(n, 1) + d);
            g[b].erase({a, c});
            g[a].insert({b, c});
        // }
        // else {
        //     int A = min(dist[1][n], dist[1][b] + c + dist[a][n]);
        //     int B = min(dist[n][1], dist[n][b] + c + dist[a][1]);
        //     if (A < linf && B < linf) {
        //         ans = min(ans, A + B + d);
        //     }
        // }
    }

    cout << (ans==linf?-1:ans) << endl;
}

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

    int t = 1;
    // cin >> t; 
    while (t--) {
        sol();
    }
    return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 0 / 11
• Subtask 3: 0 / 21
• Subtask 4: 0 / 63