Submission #939431

#	Time	Username	Problem	Language	Result	Execution time	Memory
939431		Gromp15	Love Polygon (BOI18_polygon)	C++17	100 / 100	300 ms	19916 KiB

polygon

#include <bits/stdc++.h>
#define ll long long
#define ar array
#define db double
#define all(x) x.begin(), x.end()
#define sz(x) (int)x.size()
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define rint(l, r) uniform_int_distribution<int>(l, r)(rng)
template<typename T> bool ckmin(T &a, const T &b) { return a > b ? a = b, 1 : 0; }
template<typename T> bool ckmax(T &a, const T &b) { return a < b ? a = b, 1 : 0; }
void test_case() {
	int n; cin >> n;
	map<string, int> mp;
	vector<int> a(n);
	vector<vector<int>> adj2(n);
	vector<int> indeg(n);
	for (int i = 0; i < n; i++) {
		string s, t;
		cin >> s >> t;
		if (!mp.count(s)) mp[s] = mp.size();
		if (!mp.count(t)) mp[t] = mp.size();
		a[mp[s]] = mp[t];
		adj2[mp[s]].push_back(mp[t]);
		adj2[mp[t]].push_back(mp[s]);
		indeg[mp[t]]++;
	}
	if (n & 1) {
		cout << -1 << '\n'; return;
	}
	vector<bool> vis(n), dir(n), vis3(n), in_ccl(n);
	for (int i = 0; i < n; i++) {
		if (i != a[i] && a[a[i]] == i) {
			dir[i] = dir[a[i]] = 1;
		}
	}
	int ans = 0, extra = 0;
	for (int i = 0; i < n; i++) if (!vis[i]) {
		vector<int> got;
		queue<int> q;
		auto dfs = [&](auto&& s, int v) -> void {
			got.emplace_back(v);
			vis[v] = 1;
			if (!indeg[v]) q.push(v);
			for (int u : adj2[v]) if (!vis[u]) s(s, u);
		};
		dfs(dfs, i);
		while (q.size()) {
			int v = q.front(); q.pop();
			if (dir[v]) {
				if (--indeg[a[v]] == 0) q.push(a[v]);
				continue;
			}
			int nxt = a[v];
			if (!dir[nxt]) {
				dir[nxt] = dir[v] = 1;
				ans++;
			}
			else {
				dir[v] = 1;
				extra++;
				// we need to find someone else
			}
			if (--indeg[nxt] == 0) q.push(nxt);
		}
		int to = i;
		while (!vis3[to]) vis3[to] = 1, to = a[to];
		while (!in_ccl[to]) in_ccl[to] = 1, to = a[to];
		int starting = -1, sx = -1;
		for (int v : got) if (in_ccl[v]) {
			sx = v;
			if (dir[v] && !dir[a[v]]) {
				starting = v; break;
			}
		}
		// if we dont have, then arbitrary is fine
		assert(~sx);
		if (!~starting) starting = sx;
		int v = starting;
		for (int i = 0; i < sz(got); i++, v = a[v]) if (!dir[v]) {
			int nxt = a[v];
			if (v == nxt) {
				dir[v] = 1;
				extra++; continue;
			}
			if (!dir[nxt]) {
				dir[nxt] = dir[v] = 1;
				ans += a[nxt] != v;
			}
			else { 
				dir[v] = 1;
				extra++;
			}
		}
	}
	cout << ans + extra << '\n';



}
int main() {
    cin.tie(0)->sync_with_stdio(0);
    int t = 1;
//    cin >> t;
    while (t--) test_case();
}

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