Submission #999181

#	Time	Username	Problem	Language	Result	Execution time	Memory
999181		vjudge1	LOSTIKS (INOI20_lostiks)	C++17	23 / 100	2079 ms	101716 KiB

Main

#include <bits/stdc++.h>

using namespace std;

#define int long long
#define inf 0x3F3F3F3F3F3F3F3F

struct DSU
{
	vector<int> e;
	void init(int n)
	{
		e.assign(n + 1, -1);
	}
	int get(int x)
	{
		if (e[x] < 0) return x;
		return e[x] = get(e[x]);
	}
	void unite(int x, int y)
	{
		x = get(x), y = get(y);
		if (x == y) return;
		if (e[x] > e[y]) swap(x, y);
		e[x] += e[y];
		e[y] = x;
	}
};

const int MXN = 1e6 + 5;
const int LOG = 20;

int n, S, T, A, B, b = 0;
vector<int> adj[MXN];
int p[LOG][MXN], dep[MXN], in[MXN], out[MXN], tim;
int id[MXN];

void dfs(int a)
{
	in[a] = ++tim;
	for (int &v : adj[a])
	{
		if (v == p[0][a]) continue;
		p[0][v] = a;
		dep[v] = dep[a] + 1;
		dfs(v);
	}
	out[a] = tim;
}

vector<array<int, 3>> m;

int anc(int u, int v)
{
	return in[u] <= in[v] && out[v] <= out[u];
}
int LCA(int u, int v)
{
	if (anc(u, v)) return u;
	if (anc(v, u)) return v;
	for (int i = LOG - 1; i >= 0; i--)
	{
		if (anc(p[i][u], v)) continue;
		u = p[i][u];
	}
	return p[0][u];
}
int DIST(int u, int v)
{
	return dep[u] + dep[v] - 2 * dep[LCA(u, v)];
}

signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cin >> n >> S >> T;
	DSU dsu;
	dsu.init(n);
	for (int i = 1; i < n; i++)
	{
		int u, v, w;
		cin >> u >> v >> w;
		adj[u].push_back(v);
		adj[v].push_back(u);
		if (!w) dsu.unite(u, v);
		else m.push_back({u, v, w});
	}
	p[0][S] = S;
	dfs(S);
	for (array<int, 3> &i : m) if (p[0][i[0]] == i[1]) swap(i[0], i[1]);
	A = dsu.get(S), B = dsu.get(T);
	int ASD = 0;
	for (int i = 1; i <= n; i++)
	{
		if (dsu.get(i) == i) id[i] = ++ASD;
	}
	for (int i = 1; i < LOG; i++) for (int j = 1; j <= n; j++) p[i][j] = p[i - 1][p[i - 1][j]];
	vector<int> o(m.size());
	iota(o.begin(), o.end(), 0);
	int res = inf;
	while (1)
	{
		DSU d;
		d.init(ASD);
		int f = 1, cur = S, ans = 0;
		for (int &i : o)
		{
			if (d.get(id[A]) == d.get(id[B])) break;
			if (d.get(id[dsu.get(m[i][0])]) != d.get(id[A]) || d.get(id[dsu.get(m[i][2])]) != d.get(id[A]))
			{
				f = 0;
				break;
			}
			d.unite(id[dsu.get(m[i][1])], id[A]);
			ans += DIST(cur, m[i][2]) + DIST(m[i][2], m[i][0]);
			cur = m[i][0];
		}
		if (f && d.get(id[A]) == d.get(id[B])) 
		{
			res = min(res, ans + DIST(cur, T));
		}
		if (!next_permutation(o.begin(), o.end())) break;
	}
	cout << (res >= inf ? -1 : res) << '\n';
}

• Subtask 1: 23 / 23
• Subtask 2: 0 / 36
• Subtask 3: 0 / 41