Submission #758231

#	Time	Username	Problem	Language	Result	Execution time	Memory
758231		jasmin	Olympic Bus (JOI20_ho_t4)	C++17	100 / 100	993 ms	4208 KiB

ho_t4

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

const ll INF=1e17;
vector<int> c;
vector<int> d;

struct graph{
    vector<vector<pair<int,int> > >adi;

    graph(int n, int m){
        adi.assign(n, {});
    }

};

void dijkstra(int start, vector<ll>& dist, vector<int>& par, int n, graph& g){

    dist.assign(n, INF);
    par.assign(n, -1);
    vector<bool> vis(n, false);
    priority_queue<pair<int,int> > pq;

    dist[start]=0;
    pq.push({-0, start});

    while(!pq.empty()){
        int v=pq.top().second;
        pq.pop();

        if(vis[v]){
            continue;
        }
        vis[v]=true;

        for(auto [u, ind]: g.adi[v]){

            if(dist[v]+c[ind] < dist[u]){
                par[u]=ind;
                dist[u] = dist[v] + c[ind];
                pq.push({-dist[u], u});
            }

        }
    }

}

vector<int> find_sp(int a, int b, vector<int>& par, vector<pair<int,int> >& edge, int m){
    vector<int> p;
    if(par[b]==-1){
        return {};
    }
    
    int v=b;
    while(v!=a){

        p.push_back(par[v]);
        v=edge[par[v]].first;
    }

    reverse(p.begin(), p.end());
    return p;
}

signed main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int n, m;
    cin >> n >> m;
    c.assign(m, 0);
    d.assign(m, 0);
    graph g(n, m);
    graph rev(n, m);
    vector<pair<int,int> > edge(m);
    for(int i=0; i<m; i++){
        int a, b;
        cin >> a >> b >> c[i] >> d[i];

        a--; b--;
        g.adi[a].push_back({b, i});
        rev.adi[b].push_back({a, i});

        edge[i]={a, b};
    }

    //distances
    vector<int> par0(n, -1);
    vector<ll> to0(n, INF);
    dijkstra(0, to0, par0, n, rev);
    vector<ll> from0(n, INF);
    dijkstra(0, from0, par0, n, g);

    vector<int> parn(n, -1);
    vector<ll> ton(n, INF);
    dijkstra(n-1, ton, parn, n, rev);
    vector<ll> fromn(n, INF);
    dijkstra(n-1, fromn, parn, n, g);


    //paths
    vector<int> path1=find_sp(0, n-1, par0, edge, m);
    vector<int> path2=find_sp(n-1, 0, parn, edge, m);
    
    vector<bool> used(m, false);
    for(auto e: path1){
        used[e]=true;
    }
    for(auto e: path2){
        used[e]=true;
    }


    //possibility 0: turning no edge
    ll ans=INF;
    ans = min(ans, from0[n-1] + fromn[0]);

    //possibility 1: edge not on path
    for(int i=0; i<m; i++){
        if(used[i]) continue;

        auto [a, b]=edge[i];

        ll d1=min(from0[b] + c[i] + ton[a], from0[n-1]);
        ll d2=min(fromn[b] + c[i] + to0[a], fromn[0]);

        ll dis=d1 + d2 + d[i];

        ans=min(ans, dis);
    }

    //possibility 2: edge on path
    for(int e=0; e<m; e++){
        if(!used[e]) continue;

        graph neu(n, m);
        for(int i=0; i<m; i++){

            auto [a, b]=edge[i];
            if(i==e){
                neu.adi[b].push_back({a, i});
            }
            else{
                neu.adi[a].push_back({b, i});
            }
        }

        ll dis=d[e];
        vector<ll> dist(n, INF);
        vector<int> p(n, -1);
        dijkstra(0, dist, p, n, neu);
        dis += dist[n-1];

        dijkstra(n-1, dist, p, n, neu);
        dis+=dist[0];

        ans=min(ans, dis);
    }

    //output
    if(ans==INF){
        cout << -1 << "\n";
    }
    else{
        cout << ans << "\n";
    }
}

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