Submission #1083765

#	Time	Username	Problem	Language	Result	Execution time	Memory
1083765		IBory	Love Polygon (BOI18_polygon)	C++17	100 / 100	149 ms	23656 KiB

polygon

#include <bits/stdc++.h>
#define pii pair<int, int>
using namespace std;

const int MAX = 100007;
pair<string, string> E[MAX];
int F[MAX], V[MAX], in[MAX], S[MAX];
vector<int> G[MAX];

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

	if (N & 1) {
		cout << -1;
		return 0;
	}

	map<string, int> SN;
	for (int i = 1; i <= N; ++i) {
		string a, b;
		cin >> a >> b;
		SN[a] = i;
		E[i] = {a, b};
	}
	for (int i = 1; i <= N; ++i) F[SN[E[i].first]] = SN[E[i].second];

	int RN = 0, match = 0;
	for (int i = 1; i <= N; ++i) {
		if (i != F[i] && F[F[i]] == i) V[i] = 1;
		else RN++;
	}
	for (int i = 1; i <= N; ++i) {
		if (V[i] || V[F[i]]) continue;
		G[i].push_back(F[i]);
		in[F[i]]++;
	}
	
	queue<int> Q;
	for (int i = 1; i <= N; ++i) if (!G[i].empty() && !in[i]) Q.push(i);

	while (!Q.empty()) {
		int cur = Q.front(); Q.pop();
		if (V[F[cur]]) continue;
		if (!S[cur] && !S[F[cur]]) {
			match++;
			S[cur] = S[F[cur]] = 1;
		}
		if (!--in[F[cur]]) Q.push(F[cur]);
	}

	for (int i = 1; i <= N; ++i) {
		if (!in[i]) continue;
		int cur = i;
		vector<int> C = {S[cur]};
		while (1) {
			cur = F[cur];
			in[cur]--;
			if (cur == i) break;
			C.push_back(S[cur]);
		}

		bool one = (*max_element(C.begin(), C.end()) == 1);
		if (!one) match += C.size() / 2;
		else {
			int piv = max_element(C.begin(), C.end()) - C.begin();
			for (int i = 0; i < C.size(); ++i) {
				int a = (piv + i) % C.size(), b = (piv + i + 1) % C.size();
				if (!C[a] && !C[b]) {
					match++;
					C[a] = C[b] = 1;
				}
			}
		}
	}

	int ans = RN - match;
	cout << ans;
	return 0;
}

Compilation message (stderr)

polygon.cpp: In function 'int main()':
polygon.cpp:68:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   68 |    for (int i = 0; i < C.size(); ++i) {
      |                    ~~^~~~~~~~~~

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