Submission #599371

#	Time	Username	Problem	Language	Result	Execution time	Memory
599371		pedroslrey	Railway (BOI17_railway)	C++17	100 / 100	213 ms	26832 KiB

railway

#include <bits/stdc++.h>

using namespace std;

const int MAXN = 1e5 + 10;
const int MAXK = 20;

vector<pair<int, int>> graph[MAXN];
int dp[MAXN][MAXK];
int prof[MAXN], sub[MAXN], idx[MAXN], in[MAXN], out[MAXN], order[MAXN];
int tempo;

void dfs_lca(int u, int p) {
    in[u] = ++tempo;
    order[tempo] = u;
    for (auto [v, id]: graph[u]) {
        if (v == p) continue;

        dp[v][0] = u;
        for (int k = 1; k < MAXK; ++k)
            dp[v][k] = dp[dp[v][k-1]][k-1];
        prof[v] = prof[u] + 1;

        dfs_lca(v, u);
    }
    out[u] = tempo;
}

int lca(int a, int b) {
    if (prof[b] > prof[a]) swap(a, b);

    int d = prof[a] - prof[b];
    for (int k = 0; k < MAXK; ++k)
        if (d & (1 << k)) a = dp[a][k];

    if (a == b) return a;

    for (int k = MAXK - 1; k >= 0; --k)
        if (dp[a][k] != dp[b][k]) {
            a = dp[a][k];
            b = dp[b][k];
        }

    return dp[a][0];
}

void dfs_sub(int u, int p) {
    for (auto [v, id]: graph[u])
        if (v != p) {
            idx[v] = id;
            dfs_sub(v, u);
            sub[u] += sub[v];
        }
}

int main() {
    int n, m, k;
    cin >> n >> m >> k;

    for (int i = 1; i <= n-1; ++i) {
        int u, v;
        cin >> u >> v;

        graph[u].emplace_back(v, i);
        graph[v].emplace_back(u, i);
    }

    dfs_lca(1, 1);

    for (int i = 0; i < m; ++i) {
        int s;
        cin >> s;

        vector<int> xs(s);
        for (int &x: xs)
            cin >> x;

        sort(xs.begin(), xs.end(), [&](int a, int b) { return in[a] < in[b]; });

        vector<int> lcas;
        for (int i = 0; i < s-1; ++i)
            lcas.push_back(lca(xs[i], xs[i + 1]));

        sort(lcas.begin(), lcas.end(), [&](int a, int b) { return prof[a] > prof[b]; });
        lcas.erase(unique(lcas.begin(), lcas.end()), lcas.end());

        set<int> atual;
        for (int x: xs)
            atual.insert(in[x]);

        for (int u: lcas) {
            auto beg = atual.lower_bound(in[u]);
            auto ed  = atual.upper_bound(out[u]);

            vector<int> tmp;
            while (beg != ed) {
                ++sub[order[*beg]];
                --sub[u];
                tmp.push_back(*beg);
                ++beg;
            }

            for (int v: tmp)
                atual.erase(v);
            atual.insert(in[u]);
        }
    }

    dfs_sub(1, 1);

    vector<int> ans;
    for (int i = 1; i <= n; ++i)
        if (sub[i] >= k) ans.push_back(idx[i]);
    sort(ans.begin(), ans.end());

    cout << ans.size() << "\n";
    for (int x: ans)
        cout << x << " ";
    cout << "\n";
}

• Subtask 1: 8 / 8
• Subtask 2: 15 / 15
• Subtask 3: 7 / 7
• Subtask 4: 29 / 29
• Subtask 5: 16 / 16
• Subtask 6: 25 / 25