Submission #374693

#	Time	Username	Problem	Language	Result	Execution time	Memory
374693		morato	Love Polygon (BOI18_polygon)	C++17	25 / 100	481 ms	32644 KiB

polygon

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

const int N = 1e5 + 5;

map<string, int> id;
string a[N], b[N];
vector<int> adj[N];
vector<vector<int>> cicles, pontas;
int prv[N], vis[N], in[N], n_cicle[N], n_ponta[N], leads[N];
int cnt_cicles, cnt_pontas;
bool used[N]; // if a cicle was matched with a 'ponta'

void get_cicles(int v) {
	vis[v] = 1;
	for (int u : adj[v]) {
		if (!vis[u]) {
			prv[u] = v;
			get_cicles(u);
		} else if (vis[u] == 1) {
			cicles.push_back({v});
			n_cicle[v] = ++cnt_cicles;
			int cur  = v;
			while (cur != u) {
				cur = prv[cur];
				n_cicle[v] = cnt_cicles;
				cicles.back().push_back(cur);
			}
			cnt_cicles++;
		}
	}
	vis[v] = 2;
}

void get_pontas(int v) {
	for (int u : adj[v]) {
		if (n_cicle[u]) {
			leads[n_ponta[v]] = n_cicle[u];
		} else {
			n_ponta[u] = n_ponta[v];
			pontas.back().push_back(u);
			get_pontas(u);
		}
	}
}

int main() {
	int n; cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> a[i] >> b[i];
		id[a[i]], id[b[i]];
	}
	if (n & 1) {
		cout << -1 << '\n';
		return 0;
	}
	int cnt = 0;
	for (auto it = id.begin(); it != id.end(); it++) {
		it->second = ++cnt;
	}
	for (int i = 0; i < n; i++) {
		adj[id[a[i]]].push_back(id[b[i]]);
		in[id[b[i]]]++;
	}
	for (int i = 1; i <= n; i++) {
		if (!vis[i]) {
			get_cicles(i);
		}	
	}
	for (int i = 1; i <= n; i++) {
		if (!in[i]) {
			pontas.push_back({i});
			n_ponta[i] = ++cnt_pontas;
			get_pontas(i);
		}
	}
	int ans = 0;
	for (int i = 0; i < (int) pontas.size(); i++) {
		if ((int) pontas[i].size() % 2 != 0 && (int) cicles[leads[i + 1] - 1].size() % 2 != 0) {
			pontas[i].pop_back();
			cicles[leads[i + 1] - 1].pop_back();
		}
		// cout << (int) pontas[i].size() << '\n';
		ans += ((int) pontas[i].size() + 1) / 2;
	}
	for (int i = 0; i < (int) cicles.size(); i++) {
		// cout << (int) cicles[i].size() << '\n';
		ans += ((int) cicles[i].size() == 2 ? 0 : ((int) cicles[i].size() + 1) / 2);
	}
	cout << ans << '\n';
}

• Subtask 1: 0 / 21
• Subtask 2: 25 / 25
• Subtask 3: 0 / 29
• Subtask 4: 0 / 25