Submission #1141142

#	Time	Username	Problem	Language	Result	Execution time	Memory
1141142		buzdi	Commuter Pass (JOI18_commuter_pass)	C++17	100 / 100	418 ms	21284 KiB

commuter_pass

#include <bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
#define ll long long
#define ld long double

using namespace std;
using namespace __gnu_pbds;

typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;

const int NMAX = 1e5;
const ll INF = 1e18;

struct PQElement {
    int node, parent;
    ll d;
    bool operator < (const PQElement &other) const {
        return other.d < d;
    }
};

int n, m, s, t, x, y;
ll answer;
vector<pair<int, int>> g[NMAX + 1];
vector<int> g1[NMAX + 1];
int indegree[NMAX + 1];
ll dp[NMAX + 1];
ll d[4][NMAX + 1];

void Dijkstra(int start, int which_start) {
    for(int i = 1; i <= n; i++) {
        d[which_start][i] = INF;
    }
    
    priority_queue<PQElement> pq;
    pq.push({start, 0, 0});
    while(!pq.empty()) {
        auto [node, parent, curent_d] = pq.top();
        pq.pop();

        if(d[which_start][node] == INF) {
            d[which_start][node] = curent_d;
            for(auto [next_node, edge_d] : g[node]) {
                pq.push({next_node, node, curent_d + edge_d});
            }
        } 
    }
}

// void DijkstraDP(int start, int finish) {
//     for(int i = 0; i <= n; i++) {
//         d[2][i] = INF;
//         dp[i] = INF;
//     }

//     priority_queue<PQElement> pq;
//     pq.push({start, 0, 0});
//     d[2][start] = 0;
//     dp[start] = d[0][start];
//     while(!pq.empty()) {
//         auto [node, parent, curent_d] = pq.top();
//         pq.pop();

//         answer = min(answer, dp[node] + d[1][node]);
//         if(node == finish) {
//             return;
//         }

//         if(d[2][node] != curent_d) {
//             continue;
//         }

//         for(auto [next_node, edge_d] : g[node]) {
//             int next_d = curent_d + edge_d;
//             if(next_d < d[2][next_node]) {
//                 d[2][next_node] = next_d;
//                 dp[next_node] = min(dp[node], d[0][next_node]);
//                 pq.push({next_node, node, next_d});
//             }
//             else if(next_d == d[2][next_node]) {
//                 dp[next_node] = min(dp[next_node], dp[node]);
//             }
//         }
//     }
// }

void SolveDP0() {
    for(int i = 1; i <= n; i++) {
        indegree[i] = 0;
    }

    for(int i = 1; i <= n; i++) {
        for(auto [j, edge_d] : g[i]) {
            if(d[2][i] + edge_d + d[3][j] == d[2][t]) {
                g1[i].push_back(j);
                indegree[j]++;
            }
        }
    }

    for(int i = 1; i <= n; i++) {
        dp[i] = d[0][i];
    }

    queue<int> q;
    for(int i = 1; i <= n; i++) {
        if(!indegree[i]) {
            q.push(i);
        }
    }

    while(!q.empty()) {
        int node = q.front();
        q.pop();

        answer = min(answer, dp[node] + d[1][node]);

        for(int next_node : g1[node]) {
            indegree[next_node]--;
            dp[next_node] = min(dp[next_node], dp[node]);
            if(!indegree[next_node]) {
                q.push(next_node);
            }
        }
    }
}

void SolveDP1() {
    for(int i = 1; i <= n; i++) {
        indegree[i] = 0;
    }

    for(int i = 1; i <= n; i++) {
        for(auto [j, edge_d] : g[i]) {
            if(d[3][i] + edge_d + d[2][j] == d[3][s]) {
                g1[i].push_back(j);
                indegree[j]++;
            }
        }
    }

    for(int i = 1; i <= n; i++) {
        dp[i] = d[0][i];
    }

    queue<int> q;
    for(int i = 1; i <= n; i++) {
        if(!indegree[i]) {
            q.push(i);
        }
    }

    while(!q.empty()) {
        int node = q.front();
        q.pop();

        answer = min(answer, dp[node] + d[1][node]);

        for(int next_node : g1[node]) {
            indegree[next_node]--;
            dp[next_node] = min(dp[next_node], dp[node]);
            if(!indegree[next_node]) {
                q.push(next_node);
            }
        }
    }
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    cin >> n >> m >> s >> t >> x >> y;
    for(int i = 1; i <= m; i++) {
        int a, b, c;
        cin >> a >> b >> c;
        g[a].emplace_back(b, c);
        g[b].emplace_back(a, c);
    }

    Dijkstra(x, 0);
    Dijkstra(y, 1);
    Dijkstra(s, 2);
    Dijkstra(t, 3); 

    answer = INF;
    SolveDP0();
    SolveDP1();
    cout << answer << '\n';

    return 0;
}

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