Submission #958506

#	Time	Username	Problem	Language	Result	Execution time	Memory
958506		BhavayGoyal	Olympic Bus (JOI20_ho_t4)	C++14	37 / 100	1026 ms	5104 KiB

ho_t4

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

#define int unsigned int
#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 inf = 2e9;

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

const int N = 201, M = 50001;
int n, m, aa[M], bb[M], cc[M], dd[M], dis[N], vis[N], dist[N][N], isShort[M];
set<pii> g[N];

void dijkstra(int source) {
    priority_queue<pii, vector<pii>, greater<>> q;
    vi vis(n+1, 0), dis(n+1, inf), par(n+1), idx(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 = cc[child.s];
            if (dis[src] < inf && dis[ch] > dis[src] + wt) {
                par[ch] = src;
                idx[ch] = child.s;
                dis[ch] = dis[src] + wt;
                q.push({dis[ch], ch});
            }
        }
    }

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

int get_dist(int s, int t) {
    for (int i = 1; i <= n; i++) dis[i] = inf, vis[i] = 0;
    priority_queue<pii, vector<pii>, greater<>> q;
    q.push({0, s});
    dis[s] = 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 = cc[child.s];
            if (dis[src] < inf && dis[ch] > dis[src] + wt) {
                dis[ch] = dis[src] + wt;
                q.push({dis[ch], ch});
            }
        }
    }

    return dis[t];
}


void sol() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++) for (int j = 1; j <= n; j++) if (i != j) dist[i][j] = inf;

    for (int i = 1; i <= m; i++) {
        cin >> aa[i] >> bb[i] >> cc[i] >> dd[i];
        dist[aa[i]][bb[i]] = min(dist[aa[i]][bb[i]], cc[i]);
        g[aa[i]].insert({bb[i], i});
    }

    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) {
                if (dist[i][k] < inf && dist[k][j] < inf)
                    dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
            }
        }
    }

    int ans = inf;
    if (dist[1][n] < inf && dist[n][1] < inf) ans = dist[1][n] + dist[n][1];

    for (int i = 1; i <= m; i++) {
        int a = aa[i], b = bb[i], c = cc[i], d = dd[i];
        if (isShort[i]) {
            g[a].erase(g[a].find({b, i}));
            g[b].insert({a, i});
            int x = get_dist(1, n), y = get_dist(n, 1);
            if (x < inf && y < inf)
                ans = min(ans, x + y + d);
            g[b].erase(g[b].find({a, i}));
            g[a].insert({b, i});
        }
        else {
            int A = dist[1][n];
            int B = dist[n][1]; 
            if (dist[1][b] < inf && dist[a][n] < inf) A = min(A, dist[1][b] + c + dist[a][n]);
            if (dist[n][b] < inf && dist[a][1] < inf) B = min(B, dist[n][b] + c + dist[a][1]);
            if (A < inf && B < inf)
                ans = min(ans, A + B + d);
        }
    }

    if (ans == inf) cout << "-1" << endl;
    else cout << 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: 11 / 11
• Subtask 3: 21 / 21
• Subtask 4: 0 / 63