Submission #298033

#	Time	Username	Problem	Language	Result	Execution time	Memory
298033		miss_robot	Railway (BOI17_railway)	C++14	100 / 100	370 ms	50164 KiB

railway

#include <bits/stdc++.h>

#pragma GCC optimize("O3")

using namespace std;

const int N = 1e5, L = 17;
int n, m, k;
vector<int> g[N], ind[N], sol, llca[N];
int up[N], p[L][N], h[N];
set<int> qry[N];

void dfs(int u, int l, int d){
	p[0][u] = l;
	h[u] = d++;
	for(int i = 0, v; i < (int)g[u].size(); i++){
		v = g[u][i];
		if(v == l) up[u] = ind[u][i];
		else dfs(v, u, d);
	}
}

int kth(int u, int k){
	for(int i = L-1; i >= 0; i--)
		if(k >= (1<<i))
			k -= (1<<i), u = p[i][u];
	return u;
}

int lca(int u, int v){
	if(h[v] > h[u]) swap(u, v);
	u = kth(u, h[u]-h[v]);
	if(u == v) return u;
	for(int i = L-1; i >= 0; i--)
		if(p[i][u] != p[i][v])
			u = p[i][u], v = p[i][v];
	return p[0][u];
}

void solve(int u){
	for(int v : g[u]){
		if(v == p[0][u]) continue;
		solve(v);
		if(qry[v].size() > qry[u].size()) swap(qry[u], qry[v]);
		qry[u].insert(qry[v].begin(), qry[v].end());
	}
	for(int &x : llca[u]) qry[u].erase(x);
	if((int)qry[u].size() >= k) sol.push_back(up[u]);
}

int main(){
	cin.tie(0);
	ios::sync_with_stdio(0);
	cin >> n >> m >> k;
	for(int i = 1, u, v; i < n; i++){
		cin >> u >> v;
		u--, v--;
		g[u].push_back(v);
		g[v].push_back(u);
		ind[u].push_back(i);
		ind[v].push_back(i);
	}
	dfs(0, 0, 0);
	for(int i = 1; i < L; i++)
		for(int j = 0; j < n; j++)
			p[i][j] = p[i-1][p[i-1][j]];
	while(m--){
		int s, a, b;
		cin >> s >> b;
		b--;
		qry[b].insert(m);
		while(--s){
			cin >> a;
			a--;
			b = lca(b, a);
			qry[a].insert(m);
		}
		llca[b].push_back(m);
	}
	solve(0);
	sort(sol.begin(), sol.end());
	cout << sol.size() << "\n";
	for(int &x : sol) 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