Submission #667177

#	Time	Username	Problem	Language	Result	Execution time	Memory
667177		Kahou	Railway (BOI17_railway)	C++14	100 / 100	112 ms	24780 KiB

railway

#include<bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define endl '\n'
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int N = 1e5 + 50;
int n, m, k, out[N], par[20][N], h[N], st[N], ft[N], t, p[N];
pii E[N];
vector<int> adj[N];
vector<int> vc;

void dfs(int u, int p) {
	st[u] = ++t;
	par[0][u] = p;
	h[u] = h[p]+1;
	for (int v:adj[u]) {
		if (v == p) continue;
		dfs(v, u);
	}
	ft[u] = t;
}

int Par(int u, int k) {
	for (int i = 0; i < 20; i++) {
		if (k>>i&1) u = par[i][u];
	}
	return u;
}

int LCA(int u, int v) {
	if (h[u] < h[v]) swap(u, v);
	u = Par(u, h[u]-h[v]);
	if (u == v) return u;

	for (int i = 19; i >= 0; i--) {
		if (par[i][u] != par[i][v]) {
			u = par[i][u];
			v = par[i][v];
		}
	}
	return par[0][u];
}

void dfs2(int u, int p) {
	for (int v:adj[u]) {
		if (v == p) continue;
		dfs2(v, u);
		out[u]+= out[v];
	}
}

bool cmp(int u, int v) {
	return st[u] < st[v];
}

void solve() {
	cin >> n >> m >> k;
	for (int i=1; i <= n-1; i++) {
		int u,v;
		cin >> u >> v;
		E[i] = {u, v};
		adj[u].push_back(v);
		adj[v].push_back(u);
	}
	dfs(1,0);
	for (int k = 1; k < 20; k++) {
		for (int u = 1; u <= n; u++) {
			par[k][u] = par[k-1][par[k-1][u]];
		}
	}

	while (m--) {
		vc.clear();
		int s;
		cin >> s;
		for (int i = 1; i <= s; i++) {
			int u;
			cin >> u;
			vc.push_back(u);
		}
		sort(vc.begin(), vc.end(), cmp);
		for (int i = 1; i < s; i++) {
			vc.push_back(LCA(vc[i-1], vc[i]));
		}
		sort(vc.begin(), vc.end(), cmp);
		vc.resize(unique(vc.begin(), vc.end()) - vc.begin());
		
		p[vc[0]] = 0;
		for (int i = 1; i < (int)vc.size(); i++) {
			int u = vc[i];
			p[u] = vc[i-1];
			while (p[u] > 0 && ft[p[u]] < ft[u]) p[u] = p[p[u]];
			out[u]++, out[p[u]]--;
		}
	}
	dfs2(1, 0);
	int ans = 0;
	for (int i = 1; i <= n-1; i++) {
		if (par[0][E[i].S] == E[i].F) swap(E[i].F, E[i].S);
		if (out[E[i].F] >= k) ans++;
	}
	cout << ans << endl;
	for (int i = 1; i <= n-1; i++) {
		if (out[E[i].F] >= k) cout << i << ' ';
	}
	cout << endl;
}
int main() {
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	solve();
	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