Submission #1243634

#	Time	Username	Problem	Language	Result	Execution time	Memory
1243634		longgggg	Commuter Pass (JOI18_commuter_pass)	C++20	15 / 100	2095 ms	55236 KiB

commuter_pass

#include <bits/stdc++.h>
#define Longgggg ios_base::sync_with_stdio(0); cin.tie(0);
#define ll long long
#define endl '\n'
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 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 IN "A.in"
#define OUT "A.out"
#define DEBUG "debug.out"


const int INF = (int) 1e9+5;
const ll LINF = (ll) 1e18;
const ll MOD = (ll) 1e9+7;
const int mxN = 200005;

int n, m, S, T, U, V;
vector <pair <ll, ll>> adj[mxN];
vector <ll> d(mxN), par(mxN);
set <pair <ll, ll>> path;

// Chỉ dành cho N, M nhỏ!
void solve() {
    cin >> n >> m >> S >> T >> U >> V;
    vector<vector<pair<int, int>>> adj(n+1);
    vector<tuple<int,int,int>> edges;
    for (int i = 0; i < m; ++i) {
        int u, v, w; cin >> u >> v >> w;
        adj[u].push_back({v, w});
        adj[v].push_back({u, w});
        edges.emplace_back(u, v, w);
    }
    // 1. Dijkstra S->T
    vector<ll> ds(n+1, LINF), par(n+1, -1);
    priority_queue<pair<ll,int>, vector<pair<ll,int>>, greater<>> pq;
    ds[S]=0; pq.push({0, S});
    while(!pq.empty()) {
        auto [d,u] = pq.top(); pq.pop();
        if (d > ds[u]) continue;
        for (auto [v, w] : adj[u]) {
            if (ds[v] > ds[u]+w) {
                ds[v] = ds[u]+w;
                par[v] = u;
                pq.push({ds[v], v});
            }
        }
    }
    ll minST = ds[T];

    // 2. Build DAG of all shortest paths
    vector<vector<pair<int,int>>> dag(n+1);
    for (auto [u,v,w] : edges) {
        if (ds[u] + w == ds[v]) dag[u].push_back({v, w});
        if (ds[v] + w == ds[u]) dag[v].push_back({u, w});
    }

    // 3. DFS all path from S->T, for each, build set of free edge and Dijkstra U->V
    ll ans = LINF;
    vector<pair<int,int>> path;
    set<pair<int,int>> used;
    function<void(int)> dfs = [&](int u) {
        if (u == T) {
            // Mark path
            set<pair<int,int>> free;
            for (auto [x, y] : path)
                free.insert({min(x, y), max(x, y)});
            // Dijkstra U->V
            vector<ll> d(n+1, LINF);
            priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<>> pq2;
            d[U] = 0; pq2.push({0, U});
            while (!pq2.empty()) {
                auto [du, uu] = pq2.top(); pq2.pop();
                if (du > d[uu]) continue;
                for (auto [vv, ww] : adj[uu]) {
                    ll cost = free.count({min(uu, vv), max(uu, vv)}) ? 0 : ww;
                    if (d[vv] > d[uu] + cost) {
                        d[vv] = d[uu] + cost;
                        pq2.push({d[vv], vv});
                    }
                }
            }
            ans = min(ans, d[V]);
            return;
        }
        for (auto [v, w] : dag[u]) {
            if (used.count({u, v})) continue;
            used.insert({u, v});
            path.push_back({u, v});
            dfs(v);
            path.pop_back();
            used.erase({u, v});
        }
    };
    dfs(S);
    cout << ans << '\n';
}


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

    ll t = 1; 
    // cin >> t;
    while (t--) solve();
    return 0;
}

Compilation message (stderr)

commuter_pass.cpp: In function 'int main()':
commuter_pass.cpp:114:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  114 |         freopen(IN, "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~
commuter_pass.cpp:115:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  115 |         freopen(OUT, "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~
commuter_pass.cpp:116:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  116 |         freopen(DEBUG, "w", stderr);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~

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