Submission #873902

#	Time	Username	Problem	Language	Result	Execution time	Memory
873902		noiaint	Railway (BOI17_railway)	C++17	100 / 100	104 ms	28380 KiB

railway

#include <bits/stdc++.h>

using namespace std;

#define file ""

#define mp make_pair
#define fi first
#define se second
#define all(x) x.begin(), x.end()

#define getbit(x, i) (((x) >> (i)) & 1)
#define bit(x) (1LL << (x))
#define popcount __builtin_popcountll

mt19937_64 rd(chrono::steady_clock::now().time_since_epoch().count());
int rand(int l, int r) {
    return l + rd() % (r - l + 1);
}

const int N = 1e5 + 5;
const int mod = (int)1e9 + 7; // 998244353;
const int lg = 25; // lg + 1
const int oo = 1e9;
const long long ooo = 1e18;

template<class X, class Y> bool mini(X &a, Y b) {
    return a > b ? (a = b, true) : false;
}
template<class X, class Y> bool maxi(X &a, Y b) {
    return a < b ? (a = b, true) : false;
}
void add(int &a, int b) {
    a += b;
    if (a >= mod) a -= mod;
    if (a < 0) a += mod;
}

int n, q, k;
vector<pair<int, int> > adj[N];
int fin[N];
int h[N], par[N][lg + 1];
int par_id[N];
int d[N];
vector<int> ans;
int timer = 0;

void dfs(int u, int p) {
	fin[u] = ++timer;
	par[u][0] = p;
	for (int i = 1; i <= lg; ++i) par[u][i] = par[par[u][i - 1]][i - 1];
	for (auto [v, id] : adj[u]) if (v != p) {
		h[v] = h[u] + 1;
		par_id[v] = id;
		dfs(v, u);
	}
}
int lca(int u, int v) {
	if (h[u] < h[v]) swap(u, v);
	for (int i = lg; i >= 0; --i) if (h[par[u][i]] >= h[v]) u = par[u][i];
	if (u == v) return u;
	for (int i = lg; i >= 0; --i) if (par[u][i] != par[v][i]) {
		u = par[u][i];
		v = par[v][i];
	}
	return par[u][0];
}

void dfs_dis(int u, int p) {
	for (auto [v, id] : adj[u]) if (v != p) {
		dfs_dis(v, u);
		d[u] += d[v];
		if (d[v] >= 2 * k) ans.push_back(par_id[v]);
	}
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    // freopen(file".inp", "r", stdin);
    // freopen(file".out", "w", stdout);

    cin >> n >> q >> k;
    for (int i = 1; i < n; ++i) {
    	int u, v;
    	cin >> u >> v;
    	adj[u].emplace_back(v, i);
    	adj[v].emplace_back(u, i);
    }

    h[0] = -1;
    dfs(1, 0);

    while (q--) {
    	vector<int> node;
    	int num;
    	cin >> num;
    	for (int i = 0; i < num; ++i) {
    		int x;
    		cin >> x;
    		node.push_back(x);
    	}
    	if (num == 1) continue;

    	sort(all(node), [&] (int x, int y) {
    		return fin[x] < fin[y];
    	});

    	node.push_back(node.front());

    	for (int i = 0; i < num; ++i) {
    		d[node[i]]++;
    		d[node[i + 1]]++;
    		d[lca(node[i], node[i + 1])] -= 2;
    	}
    }

    dfs_dis(1, 0);

    sort(all(ans));
    cout << (int) ans.size() << '\n';
    for (int i : ans) cout << i << ' ';

    return 0;
}

/*
6 3 2
1 3
2 3
3 4
6 4
4 5
4 1 3 2 5
2 6 3
2 3 2

2
2 3
*/

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