Submission #1221250

#	Time	Username	Problem	Language	Result	Execution time	Memory
1221250		madamadam3	Commuter Pass (JOI18_commuter_pass)	C++20	16 / 100	310 ms	30120 KiB

commuter_pass

#include <bits/stdc++.h>

using namespace std;

#define int long long int

using pi = pair<int, int>;
using vb = vector<bool>;
using vi = vector<int>;
using vvi = vector<vi>;
using vpi = vector<pi>;
using vvpi = vector<vpi>;

struct DSU {
    int n; vector<int> par, siz;

    DSU(int N) {
        n = N;
        par.resize(n); iota(par.begin(), par.end(), 0);
        siz.assign(n, 1);
    }

    int find(int v) {
        if (v == par[v]) return v;
        return par[v] = find(par[v]);
    }

    void unite(int a, int b) {
        a = find(a); b = find(b);
        if (a != b) {
            if (siz[a] < siz[b]) swap(a, b);
            par[b] = a;
            siz[a] += siz[b];
        }
    }
};

const int MAXN = 100'001, MAXM = 200'001;
const int INF = numeric_limits<int>::max();
int n, m, X[MAXM], Y[MAXM], C[MAXM];
int S, T, U, V;
vi adj[MAXN], mst_adj[MAXN];

void dijkstra(int u, vi &dist, vi &par) {
    dist.assign(n+1, INF);
    par.assign(n+1, -1);

    dist[u] = 0; par[u] = 0;
    priority_queue<pi, vector<pi>, greater<pi>> q;
    q.push({0, u});

    while (!q.empty()) {
        auto cur = q.top();
        q.pop();

        int cu = cur.second, cdist = cur.first;

        for (auto &el : adj[cu]) {
            int cv = X[el] == cu ? Y[el] : X[el];
            int vdist = C[el];

            if(dist[cu] + vdist < dist[cv]) {
                par[cv] = cu;
                dist[cv] = dist[cu] + vdist;
                q.push({dist[cu] + vdist, cv});
            }
        }
    }
}

void dfs(int u, int last_edge, int cur_dist, int shortest, vb &seen, vvi &paths, vi &par) {
    if (cur_dist > shortest) return;
    if (cur_dist == shortest && u == T) {
        vi path;
        int cur = last_edge;
        while (cur != -1) {
            path.push_back(cur);
            cur = par[cur];
        }
        
        paths.push_back(path);
        return;
    }

    seen[u] = true;

    for (auto &eid : adj[u]) {
        int v = X[eid] == u ? Y[eid] : X[eid];
        int d = C[eid];

        if (seen[v]) continue;

        par[eid] = last_edge;
        dfs(v, eid, cur_dist + d, shortest, seen, paths, par);
        par[eid] = -1;
    }

    seen[u] = false;
}

bool largest_edge(int u, int p, int target, int &le) {
    if (u == target) {
        return true;
    }

    for (auto &eid : mst_adj[u]) {
        int v = u == X[eid] ? Y[eid] : X[eid];
        if (v == p) continue;

        if (largest_edge(v, u, target, le)) {
            if (le != -1 && C[eid] <= C[le]) continue;
            le = eid;
        }
    }
}

signed main() {
    cin >> n >> m;
    cin >> S >> T >> U >> V;

    for (int i = 1; i <= m; i++) {
        cin >> X[i] >> Y[i] >> C[i];
        adj[X[i]].push_back(i);
        adj[Y[i]].push_back(i);
    }

    vi edges(m+1); iota(edges.begin(), edges.end(), 0);
    sort(edges.begin(), edges.end(), [&](int a, int b) {return C[a] < C[b];});
    auto dsu = DSU(n+1);
    for (auto &edge : edges) {
        if (dsu.find(X[edge]) == dsu.find(Y[edge])) continue;
        dsu.unite(X[edge], Y[edge]);
        mst_adj[X[edge]].push_back(edge);
        mst_adj[Y[edge]].push_back(edge);
    }

    vi sd, spar;
    dijkstra(S, sd, spar);

    vi td, tpar;
    dijkstra(T, td, tpar);

    vi vd, vpar;
    dijkstra(V, vd, vpar);

    vi nodes;
    int best = INF;
    for (int i = 1; i <= n; i++) {
        if (!(sd[i] + td[i] == sd[T])) continue;
        best = min(best, vd[i]);
    }

    cout << best;
    return 0;
}

Compilation message (stderr)

commuter_pass.cpp: In function 'bool largest_edge(long long int, long long int, long long int, long long int&)':
commuter_pass.cpp:115:1: warning: control reaches end of non-void function [-Wreturn-type]
  115 | }
      | ^

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