Submission #219585

#	Time	Username	Problem	Language	Result	Execution time	Memory
219585		socho	Railway (BOI17_railway)	C++14	100 / 100	237 ms	46952 KiB

railway

#include "bits/stdc++.h"
using namespace std;
// #define int long long
 
int n, m, k;
const int MXN = 300005;
vector<int> adj[MXN];
 
int st_start[MXN];
int st_end[MXN];
int at = 0;
 
int adder[MXN];
 
void dfs_tr(int node, int last) {
	st_start[node] = at;
	at++;
	for (int i=0; i<adj[node].size(); i++) {
		int x = adj[node][i];
		if (x == last) continue;
		dfs_tr(x, node);
	}
	st_end[node] = at;
	at++;
}
 
const int MXK = 20;
int depth[MXN];
int par[MXN][MXK];
 
void dfs_dep(int node, int last, int dep) {
	par[node][0] = last;
	depth[node] = dep;
	for (int i=1; i<MXK; i++) {
		int p = par[node][i-1];
		if (p == -1) continue;
		par[node][i] = par[p][i-1];
	}
	for (int i=0; i<adj[node].size(); i++) {
		int o = adj[node][i];
		if (o == last) continue;
		dfs_dep(o, node, dep+1);
	}
}
 
int kth_parent(int n, int k) {
	for (int i=0; i<MXK; i++) {
		if (k & (1 << i)) {
			n = par[n][i];
		}
	}
	return n;
}
 
int lca(int a, int b) {
	if (depth[a] > depth[b]) swap(a, b);
	b = kth_parent(b, depth[b]-depth[a]);
	
	// cout << a << ' ' << b << endl;
	
	if (a == b) return a;
	
	for (int i=MXK-1; i>=0; i--) {
		if (par[a][i] != par[b][i]) {
			a = par[a][i];
			b = par[b][i];
		}
	}
	return par[a][0];
}
 
bool byt(int a, int b) {
	return st_start[a] < st_start[b];
}
 
int delta[MXN];
vector<int> chosen;
int att[MXN];
 
int dfs_rec(int node, int last) {
	
	int ans = delta[node];
	
	for (int i=0; i<adj[node].size(); i++) {
		int ad = adj[node][i];
		if (ad == last) continue;
		ans += dfs_rec(ad, node);
	}
	
	return att[node] = ans;
	
}
 
signed main() {
	
	for (int i=0; i<MXN; i++) for (int j=0; j<MXK; j++) par[i][j] = -1;
	
	cin >> n >> m >> k;
	
	vector<pair<int, int> > ed;
	
	for (int i=1; i<n; i++) {
		int a, b;
		cin >> a >> b;
		adj[a].push_back(b);
		adj[b].push_back(a);
		ed.push_back(make_pair(a, b));
	}
	dfs_tr(1, -1);
	dfs_dep(1, -1, 0);
	
	int above[n+1];
	
	for (int i=0; i<n-1; i++) {
		int a = ed[i].first, b = ed[i].second;
		if (depth[a] > depth[b]) above[a] = i+1;
		else above[b] = i+1;
	}
	
	
	// for (int i=1; i<=n; i++) cout << i << ' ' << st_start[i] << ' ' << st_end[i] << endl;
	
	for (int T=0; T<m; T++) {
		
		int nm;
		cin >> nm;
		int arr[nm];
		for (int i=0; i<nm; i++) cin >> arr[i];
		
		sort(arr, arr+nm, byt);
		
		// for (int i=0; i<nm; i++) cout << arr[i] << ' '; cout << endl;
		
		vector<pair<int, int> > ranges;
		
		
		for (int i=0; i<nm; i++) {
			int a = arr[i], b = arr[(i+1)%nm];
			int l = lca(a, b);
			// cout << a << ' ' << b << ' ' << l << endl;
			delta[l] -= 2;
			delta[a]++;
			delta[b]++;
		}
		
		
	}
	
	dfs_rec(1, -1);
	
	vector<int> f;
	
	for (int i=1; i<=n; i++) {
		if (att[i] >= 2 * k) {
			f.push_back(above[i]);
		}
	}
	sort(f.begin(), f.end());
	
	cout << f.size() << endl;
	for (int i=0; i<f.size(); i++) cout << f[i] << ' ';
	cout << endl;
	
	
	
}	

Compilation message (stderr)

railway.cpp: In function 'void dfs_tr(int, int)':
railway.cpp:18:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0; i<adj[node].size(); i++) {
                ~^~~~~~~~~~~~~~~~~
railway.cpp: In function 'void dfs_dep(int, int, int)':
railway.cpp:39:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0; i<adj[node].size(); i++) {
                ~^~~~~~~~~~~~~~~~~
railway.cpp: In function 'int dfs_rec(int, int)':
railway.cpp:84:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0; i<adj[node].size(); i++) {
                ~^~~~~~~~~~~~~~~~~
railway.cpp: In function 'int main()':
railway.cpp:161:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i=0; i<f.size(); i++) cout << f[i] << ' ';
                ~^~~~~~~~~

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