Submission #817019

#	Time	Username	Problem	Language	Result	Execution time	Memory
817019		ono_de206	Parking (CEOI22_parking)	C++14	20 / 100	95 ms	16860 KiB

Main

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

#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define in insert
#define all(x) x.begin(),x.end()
#define pb push_back
#define eb emplace_back
#define ff first
#define ss second

// #define int long long
 
typedef long long ll;
typedef vector<int> vi;
typedef set<int> si;
typedef multiset<int> msi;
typedef pair<int, int> pii;
typedef vector<pii> vpii;

template<typename T, typename U>
ostream & operator << (ostream &out, const pair<T, U> &c) {
	out << c.first << ' ' << c.second;
    return out;
}

template<typename T>
ostream & operator << (ostream &out, vector<T> &v) {
	const int sz = v.size();
	for (int i = 0; i < sz; i++) {
		if (i) out << ' ';
		out << v[i];
	}
    return out;
}

template<typename T>
istream & operator >> (istream &in, vector<T> &v) {
	for (T &x : v) in >> x;
    return in;
}


template<typename T>
void mxx(T &a, T b){if(b > a) a = b;}
template<typename T>
void mnn(T &a, T b){if(b < a) a = b;}

const int mxn = 2e5 + 10;
int v[mxn][2], done[mxn];
vector<pair<int, int>> g[mxn];

void go() {
	int n, m;
	cin >> n >> m;
	set<int> em;
	for(int i = 1; i <= m; i++) {
		for(int j = 0; j < 2; j++) {
			cin >> v[i][j];
			if(v[i][j]) g[v[i][j]].eb(j, i);
		}
		if(v[i][0] == 0) em.in(i);
		else if(v[i][0] == v[i][1]) done[v[i][0]] = 1;
	}

	vector<pair<int, int>> ans;

	for(int i = 1; i <= n; i++) {
		if(done[i]) continue;
		sort(all(g[i]));
		if(g[i][0].ff == 1) {
			if(em.empty()) {
				cout << -1 << '\n';
				return;
			}
			int x = *em.begin();
			ans.eb(g[i][0].ss, x);
			ans.eb(g[i][1].ss, x);
			v[g[i][0].ss][1] = v[g[i][1].ss][1] = 0;
			em.erase(x);
			v[x][0] = v[x][1] = i;
			done[i] = 1;
		}
	}

	function<void(int)> dfs = [&](int x) -> void {
		if(done[x]) return;
		if(g[x][1].ff == 0 && v[g[x][0].ss][1] == 0 && v[g[x][1].ss][1] == 0) {
			em.in(g[x][0].ss);
			ans.eb(g[x][0].ss, g[x][1].ss);
			v[g[x][0].ss][0] = 0;
			done[x] = 1;
		} else if(g[x][1].ff == 1 && v[g[x][0].ss][1] == 0) {
			ans.eb(g[x][1].ss, g[x][0].ss);
			v[g[x][1].ss][1] = 0;
			done[x] = 1;
			dfs(v[g[x][1].ss][0]);
		}
	};

	for(int i = 1; i <= n; i++) {
		if(done[i]) continue;
		dfs(i);
	}
	for(int i = 1; i <= n; i++) {
		if(done[i]) continue;
		assert(g[i][1].ff == 1);
		int x = g[i][0].ss, y = g[i][1].ss;
		if(em.empty()) {
			cout << -1 << '\n';
			return;
		}
		int p = *em.begin();
		ans.eb(y, p);
		v[y][1] = 0;
		v[p][0] = i;
		g[i][1] = {0, p};
		dfs(v[y][0]);
	}
	for(int i = 1; i <= n; i++) {
		if(!done[i]) {
			cout << -1 << '\n';
			return;
		}
	}
	cout << ans.size() << '\n';
	for(auto it : ans) {
		cout << it << '\n';
	}
}
 
signed main() {
	// #ifndef ONO
	// freopen("file.in", "r", stdin);
	// freopen("file.out", "w", stdout);
	// #endif
	fast;
	int t = 1;
	// cin >> t;
	while(t--) {
		go();
	}
	return 0;
}

Compilation message (stderr)

Main.cpp: In function 'void go()':
Main.cpp:108:7: warning: unused variable 'x' [-Wunused-variable]
  108 |   int x = g[i][0].ss, y = g[i][1].ss;
      |       ^

• Subtask 1: 10 / 10
• Subtask 2: 10 / 10
• Subtask 3: 0 / 25
• Subtask 4: 0 / 15
• Subtask 5: 0 / 25
• Subtask 6: 0 / 15