Submission #1253889

#	Time	Username	Problem	Language	Result	Execution time	Memory
1253889		ankite	Railway (BOI17_railway)	C++20	100 / 100	63 ms	25020 KiB

railway

#include <bits/stdc++.h>
using namespace std;
void print() { cerr << '\n'; }
template<typename T, typename... Args>
void print(T first, Args... rest) {
    cerr << first << ' ';
    print(rest...);
}

const int li = 2e5 + 5;
int n, m, k;
vector<pair<int, int>> graph[li];
int tin[li], tout[li], timer = 0, anc[li][20], p_edge[li];
int chosen[li], bit[li];

void dfs(int node = 1, int parent = 0) {
    tin[node] = ++timer;
    for (int i = 1; i < 20; i++) anc[node][i] = anc[anc[node][i - 1]][i - 1];
    for (pair<int, int> i : graph[node]) {
        if (i.first != parent) {
            anc[i.first][0] = node;
            p_edge[i.first] = i.second;
            dfs(i.first, node);
        }
    }

    tout[node] = timer;
}


bool is_ancestor(int a, int b) { return (tin[a] <= tin[b] && tout[a] >= tout[b]); }

int lca(int a, int b) {
    if (is_ancestor(a, b)) return a;

    for (int i=19; ~i; i--) {
        if (anc[a][i]  &&  !is_ancestor(anc[a][i], b)) a = anc[a][i];
    }

    return anc[a][0];
}

void update(int pos, int val) {
    for (; pos <= n; pos += (pos & (-pos))) bit[pos] += val;
}

int query(int a, int b) {
    int ans = 0;
    for (; b; b -= (b & (-b))) ans += bit[b];
    for (a--; a; a -= (a & (-a))) ans -= bit[a];

    return ans;
}

signed main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    cin >> n >> m >> k;
    for (int i=1, a, b; i<=n-1; i++) {
        cin >> a >> b;
        graph[a].push_back({b, i});
        graph[b].push_back({a, i});
    }

    dfs();
    while (m--) {
//        cout << " *" << m << "\n";
        int s, l;
        cin >> s;
        for (int i=0; i<s; i++) cin >> chosen[i];
        sort(chosen, chosen + s, [](int A, int B) { return tin[A] < tin[B]; });

        chosen[s] = chosen[0];
        for (int i = 0; i < s; i++) {
            int l = lca(chosen[i], chosen[i + 1]);
            update(tin[chosen[i]], 1);
            update(tin[chosen[i + 1]], 1);
            update(tin[l], -2);
        }
    }
    vector<int> ans;
    for (int i=2; i<=n; i++)
        if (query(tin[i], tout[i]) >= 2 * k) ans.push_back(p_edge[i]);
    sort(ans.begin(), ans.end());
    cout << ans.size() << '\n';
    for (int i : ans) cout << i << ' ';
    return 0;
}

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