Submission #1243847

#	Time	Username	Problem	Language	Result	Execution time	Memory
1243847		longgggg	Commuter Pass (JOI18_commuter_pass)	C++20	0 / 100	2094 ms	26224 KiB

commuter_pass

#include <bits/stdc++.h>
using namespace std;
// ===== BITWISE ===== //
#define MASK(i) (1LL << (i))
#define BIT(x, i) (1LL & ((x) >> (i)))
#define ON(x, i) ((x) | MASK(i))
#define OFF(x, i) ((x) & ~MASK(i))
#define LASTBIT(mask) ((mask) & -(mask))
// ===== OTHER ===== //
#define Longgggg ios_base::sync_with_stdio(0); cin.tie(0);
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FORD(i, a, b) for (int i = (a); i >= (b); i--)
#define mod(x, k) ((((x) % (k)) + (k)) % (k))
#define all(x) begin(x), end(x)
#define fi first
#define se second
#define ll long long
#define endl '\n'
// ===== FILE ===== //
#define IN "A.in"
#define OUT "A.out"
#define DEBUG "debug.out"
//==================//

const ll INF = 1e18;
const int mxN = 1e5 + 5;

int N, M, S, T, U, V;
vector<tuple<int, int, int>> edges;
vector<pair<int, int>> adj[mxN];

vector<ll> dijkstra(int src) {
    vector<ll> dist(N + 1, INF);
    priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<>> pq;
    dist[src] = 0;
    pq.emplace(0, src);
    while (!pq.empty()) {
        auto [d, u] = pq.top(); pq.pop();
        if (d > dist[u]) continue;
        for (auto [v, c] : adj[u]) {
            if (dist[v] > dist[u] + c) {
                dist[v] = dist[u] + c;
                pq.emplace(dist[v], v);
            }
        }
    }
    return dist;
}

void solve() {
    cin >> N >> M;
    cin >> S >> T;
    cin >> U >> V;
    FOR(i, 1, M) {
        int a, b, c;
        cin >> a >> b >> c;
        edges.emplace_back(a, b, c);
        adj[a].emplace_back(b, c);
        adj[b].emplace_back(a, c);
    }

    vector<ll> distS = dijkstra(S);
    vector<ll> distT = dijkstra(T);
    vector<ll> distU = dijkstra(U);

    ll best = INF;

    // Xét mỗi cạnh trên đường ngắn nhất từ S -> T
    for (auto &[a, b, c] : edges) {
        bool onPath = false;
        if (distS[a] + c + distT[b] == distS[T]) onPath = true;
        if (distS[b] + c + distT[a] == distS[T]) onPath = true;
        if (!onPath) continue;

        // Tạm thời tạo graph mới với commuter pass miễn phí cho cạnh (a, b)
        vector<vector<pair<int, int>>> newAdj(N + 1);
        for (auto &[x, y, w] : edges) {
            int cost = w;
            if ((x == a && y == b) || (x == b && y == a)) cost = 0;
            newAdj[x].emplace_back(y, cost);
            newAdj[y].emplace_back(x, cost);
        }

        // Dijkstra lại từ U trong graph mới
        vector<ll> dist(N + 1, INF);
        priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<>> pq;
        dist[U] = 0;
        pq.emplace(0, U);
        while (!pq.empty()) {
            auto [d, u] = pq.top(); pq.pop();
            if (d > dist[u]) continue;
            for (auto &[v, cost] : newAdj[u]) {
                if (dist[v] > dist[u] + cost) {
                    dist[v] = dist[u] + cost;
                    pq.emplace(dist[v], v);
                }
            }
        }
        best = min(best, dist[V]);
    }

    // Ngoài ra, còn trường hợp không dùng commuter pass
    vector<ll> distNormal = dijkstra(U);
    best = min(best, distNormal[V]);

    cout << best << endl;
}

signed main() {
    if (fopen(IN, "r")) {
        freopen(IN, "r", stdin);
        freopen(OUT, "w", stdout);
        freopen(DEBUG, "w", stderr);
    }
    Longgggg

    solve();
    return 0;
}

Compilation message (stderr)

commuter_pass.cpp: In function 'int main()':
commuter_pass.cpp:111:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  111 |         freopen(IN, "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~
commuter_pass.cpp:112:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  112 |         freopen(OUT, "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~
commuter_pass.cpp:113:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  113 |         freopen(DEBUG, "w", stderr);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 16
• Subtask 2: 0 / 15
• Subtask 3: 0 / 24
• Subtask 4: 0 / 45