Submission #519999

#	Time	Username	Problem	Language	Result	Execution time	Memory
519999		Bill_00	Railway (BOI17_railway)	C++14	100 / 100	99 ms	24504 KiB

railway

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

int n, m, k;
vector<pair<int, int>> graph[100001];
int tin[100001], tout[100001], timer = 0, anc[100001][20], p_edge[100001];
int chosen[50001], bit[100001];

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;
}

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

Compilation message (stderr)

railway.cpp: In function 'int main()':
railway.cpp:55:10: warning: unused variable 'l' [-Wunused-variable]
   55 |   int s, l;
      |          ^

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