Submission #834025

#	Time	Username	Problem	Language	Result	Execution time	Memory
834025		vjudge1	Exam (eJOI20_exam)	C++17	0 / 100	4 ms	5204 KiB

exam

#include <bits/stdc++.h>
#define ll long long
#define plli pair<ll, int>

using namespace std;

const int N = 1e5 + 2;
int n, m, s, t, a, b;
vector<pair<int, ll>>adj[N];
vector<tuple<int, int, ll>>edge;
ll dist[N], distB[N];

void st1(){
    for(int i = 1; i <= n; i++) dist[i] = distB[i] = 1e18;
    priority_queue<plli, vector<plli>, greater<plli>>pq;

    //shortest path from b to all
    pq.emplace(0LL, b);
    distB[b] = 0;
    while(!pq.empty()){
        auto [curW, u] = pq.top(); pq.pop();
        for(auto &[v, w]: adj[u]){
            if(distB[v] > curW + w){
                distB[v] = curW + w;
                pq.emplace(distB[v], v);
            }
        }
    }

    //shortest path from s to t????
    pq.emplace(0LL, s);
    dist[s] = 0;
    vector<int>p[n + 1];
    while(!pq.empty()){
        auto [curW, u] = pq.top(); pq.pop();
        for(auto &[v, w]: adj[u]){
            if(dist[v] > curW + w){
                p[v].clear();
                p[v].push_back(u);
                dist[v] = curW + w;
                pq.emplace(dist[v], v);
            } else if(dist[v] == curW + w){
                p[v].push_back(u);
            }
        }
    }

    queue<int>q; q.push(t);
    ll ans = 1e18;
    while(!q.empty()){
        int cur = q.front(); q.pop();
        ans = min(ans, distB[cur]);
        for(auto &nxt: p[cur]) q.push(nxt);
    }

    cout << ans << '\n';
}

void cape(){
    vector<pair<int, ll>>adj1[N];
    int p[N];

    for(int i = 1; i <= n; i++){
        dist[i] = 1e18;
        p[i] = i;
    }

    priority_queue<plli, vector<plli>, greater<plli>>pq;
    pq.emplace(0LL, s);

    while(!pq.empty()){
        auto [curW, u] = pq.top(); pq.pop();
        for(auto &[v, w]: adj[u]){
            if(dist[v] <= curW + w) continue;
            dist[v] = curW + w;
            p[v] = u;
            pq.emplace(dist[v], v);
        }
    }

    set<pair<int, int>>st;
    int cur = t;
    while(cur != s){
        st.insert({cur, p[cur]});
        st.insert({p[cur], cur});

        cur = p[cur];
    }   

    for(auto &[u, v, w]: edge){
        if(st.count({u, v})) w = 0;
        adj1[u].emplace_back(v, w);
        adj1[v].emplace_back(u, w);
    }

    for(int i = 1; i <= n; i++) dist[i] = 1e18;

    pq.emplace(0LL, a);
    dist[a] = 0;

    while(!pq.empty()){
        auto [curW, u] = pq.top(); pq.pop();
        for(auto &[v, w]: adj1[u]){
            if(dist[v] <= curW + w) continue;
            dist[v] = curW + w;
            pq.emplace(dist[v], v);
        }
    }

    cout << dist[b] << '\n';
}

int main(){
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    cin >> n >> m >> s >> t >> a >> b;
    while(m--){
        int u, v, w; cin >> u >> v >> w;
        edge.emplace_back(u, v, w);
        adj[u].emplace_back(v, w);
        adj[v].emplace_back(u, w);
    }

    if(s == a) st1();
    else cape();

    return 0;
}

• Subtask 1: 0 / 14
• Subtask 2: 0 / 12
• Subtask 3: 0 / 13
• Subtask 4: 0 / 23
• Subtask 5: 0 / 16
• Subtask 6: 0 / 22