Submission #675685

#	Time	Username	Problem	Language	Result	Execution time	Memory
675685		vovamr	Cat (info1cup19_cat)	C++17	100 / 100	427 ms	27540 KiB

cat

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define fi first
#define se second
#define ll long long
#define ld long double
#define sz(x) ((int)(x).size())
#define all(x) 	(x).begin(), (x).end()
#define pb push_back
#define mpp make_pair
#define ve vector
using namespace std;
using namespace __gnu_pbds;
template<class T> using oset = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
const ll inf = 1e18; const int iinf = 1e9;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
template <typename T> inline bool chmin(T& a, T b) { return (a > b ? a = b, 1 : 0); }
template <typename T> inline bool chmax(T& a, T b) { return (a < b ? a = b, 1 : 0); }

inline void solve() {
	int n;
	cin >> n;
	ve<int> p(n);
	for (auto &i : p) cin >> i;

	for (int i = 0; i < n; ++i) {
		if (p[i] + p[n - i - 1] != n + 1) {
			return void(cout << -1 << '\n');
		}
	}

	ve<pii> answer;

	ve<int> pos(n + 1);
	for (int i = 0; i < n; ++i) pos[p[i]] = i;

	for (int i = 0; i < n / 2; ++i) {
		if (p[i] != i + 1 && pos[i + 1] != n - i - 1) {

			int a = i;
			int b = pos[i + 1];

			answer.pb({ i, pos[i + 1] });

			swap(p[a], p[b]);
			swap(p[n - a - 1], p[n - b - 1]);

			swap(pos[p[a]], pos[p[b]]);
			swap(pos[p[n - a - 1]], pos[p[n - b - 1]]);
		}
	}

	int cnt = 0;
	for (int i = 0; i < n / 2; ++i) {
		assert(p[i] == i + 1 || p[i] == n + 1 - (i + 1));
		cnt += (p[i] == n + 1 - (i + 1));
	}

	if (cnt & 1) {
		return void(cout << -1 << '\n');
	}

	ve<int> bad;
	for (int i = 0; i < n / 2; ++i) {
		if (p[i] == n + 1 - (i + 1)) {
			bad.pb(i);
		}
	}

	for (int i = 0; i < sz(bad); i += 2) {
		int a = bad[i];
		int b = bad[i + 1];

		answer.pb({n - a - 1, b});

		swap(p[n - a - 1], p[b]);
		swap(p[n - (n - a - 1) - 1], p[n - b - 1]);

		answer.pb({a, b});

		swap(p[a], p[b]);
		swap(p[n - a - 1], p[n - b - 1]);
	}

	cout << sz(answer) << " " << sz(answer) << '\n';
	for (auto &[i, j] : answer) cout << i + 1 << " " << j + 1 << '\n';

#ifdef LOCAL
	cout << "! "; for (auto &x : p) cout << x << " ";
	cout << "!" << '\n';
#endif
}

signed main() {
	ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
	int q = 1; cin >> q;
	while (q--) solve();
	cerr << fixed << setprecision(3) << "Time execution: " << (double)clock() / CLOCKS_PER_SEC << endl;
}

• Subtask 1: 15 / 15
• Subtask 2: 10 / 10
• Subtask 3: 25 / 25
• Subtask 4: 15 / 15
• Subtask 5: 35 / 35