Submission #311545

#	Time	Username	Problem	Language	Result	Execution time	Memory
311545		two_sides	Railway (BOI17_railway)	C++17	100 / 100	95 ms	26604 KiB

railway

#include <bits/stdc++.h>
using namespace std;

#define eb emplace_back

struct edge {
	int v, i;

	edge(int v, int i): v(v), i(i) {}
};

const int N = 1e5 + 5;
const int LG = 17;

vector <edge> adj[N];
vector <int> path, ret;
int tin[N], tim, n, m, k;
int rmq[LG][N], lg[N], ss[N];
int st[N], tp, sp[N], d[N];


void dfs(int u, int p) {
	tin[u] = tim++;
	for (edge e : adj[u])
		if (e.v != p) {
			ret.eb(tin[u]); path.eb(u);
			d[e.v] = d[u] + 1; dfs(e.v, u);
		}
}

int lca(int u, int v) {
	if (!u || !v) return u | v;
	if (u == v) return u;
	tie(u, v) = minmax(tin[u], tin[v]);
	int k = lg[v - u];
	return path[min(rmq[k][u],
		rmq[k][v - (1 << k)])];
}

void add(int u, int r) {
	ss[u]++; ss[r]--;
}

void init() {
	dfs(1, 0);
	for (int i = 0; i < n - 1; i++)
		rmq[0][i] = ret[i];
	for (int i = 2; i < n; i++)
		lg[i] = lg[i / 2] + 1;
	for (int x = 1; (1 << x) < n; x++)
		for (int i = 0; i + (1 << x) < n; i++)
			rmq[x][i] = min(rmq[x - 1][i],
			rmq[x - 1][i + (1 << (x - 1))]);
}

void vis(int u, int p) {
	for (edge e : adj[u])
		if (e.v != p) {
			vis(e.v, u); ss[u] += ss[e.v];
		}
	if (ss[u] >= k)
		for (edge e : adj[u])
			if (e.v == p) ret.eb(e.i);
}

void input() {
	cin >> n >> m >> k;
	for (int i = 1; i < n; i++) {
		int u, v; cin >> u >> v;
		adj[u].eb(v, i); adj[v].eb(u, i);
	}
}

void process() {
    auto cmp = [&](int x, int y) {
        return tin[x] < tin[y];
    };
	ret.clear();
	for (int i = 0; i < m; i++) {
		int s; cin >> s;
		st[tp = 0] = 0;
		for (int i = 0; i < s; i++) {
			cin >> sp[i];
			st[0] = lca(st[0], sp[i]);
		}
		sort(sp, sp + s, cmp);
		for (int i = 0; i < s; i++) {
			if (sp[i] == st[0]) continue;
			int r = lca(st[tp], sp[i]);
			while (tp && d[r] < d[st[tp - 1]]) {
				add(st[tp], st[tp - 1]); tp--;
			}
			if (d[r] < d[st[tp]]) add(st[tp--], r);
			if (st[tp] != r) st[++tp] = r;
			st[++tp] = sp[i];
		}
		while (tp) {
			add(st[tp], st[tp - 1]); tp--;
		}
	}
	vis(1, 0);
}

void output() {
	sort(ret.begin(), ret.end());
	cout << ret.size() << '\n';
	for (int i : ret) cout << i << ' ';
}

int main() {
	cin.tie(0)->sync_with_stdio(0);
	input(); init(); process(); output();
}

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