Submission #924665

#	Time	Username	Problem	Language	Result	Execution time	Memory
924665		Ianis	Cat (info1cup19_cat)	C++17	100 / 100	352 ms	33000 KiB

cat

#ifdef LOCAL
#include <iostream>
#include <fstream>
#include <iomanip>
#include <cassert>
#include <random>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#else
#pragma GCC optimize("Ofast,unroll-loops")
#include <bits/stdc++.h>
#define cerr if (false) cerr 
#define endl '\n'
#endif

#define fi first
#define se second

#define sz(a) ((int)(a).size())
#define all(a) (a).begin(), (a).end()

#define lsb(x) (x & (-x))

#define bit(mask, i) (((mask) >> (i)) & 1)
#define popcount(x) __builtin_popcount(x)

#define YES cout << "YES" << endl
#define NO cout << "NO" << endl

using namespace std;

template <typename T>
bool ckmax(T &a, T b) { return a < b ? a = b, true : false; }
template <typename T>
bool ckmin(T &a, T b) { return a > b ? a = b, true : false; }

using ll = long long;
using pii = pair<int, int>;

const int NMAX = 3e6+5;

int n;
int a[NMAX];
int pos[NMAX];
vector<pii> ans;
vector<pii> bad;

void read() {
   cin >> n;
   for (int i = 1; i <= n; i++) {
      cin >> a[i];
      pos[a[i]] = i;
   }
}

void my_swap(int i, int j) {
   ans.push_back({ i, j });

   swap(pos[a[i]], pos[a[j]]);
   swap(a[i], a[j]);

   swap(pos[a[n - i + 1]], pos[a[n - j + 1]]);
   swap(a[n - i + 1], a[n - j + 1]);
}

void solve() {
   ans.clear();
   bad.clear();

   for (int i = 1; i <= n / 2; i++) {
      if (a[i] != i) {
         if (a[i] == n - i + 1) {
            bad.push_back({ i, n - i + 1 });
         } else {
            my_swap(i, pos[i]);
         }
      }
   }


   for (int i = 0; i + 1 < int(bad.size()); i += 2) {
      my_swap(bad[i].fi, bad[i + 1].fi);
      my_swap(bad[i].fi, bad[i + 1].se);
   }

   for (int i = 1; i <= n; i++) {
      if (a[i] != i) {
         cout << -1 << endl;
         return;
      }
   }

   cout << ans.size() << ' ' << ans.size() << endl;
   for (auto &[ i, j ] : ans)
      cout << i << ' ' << j << endl;
}

signed main() {
#ifdef LOCAL
   freopen("input.txt", "r", stdin);
#endif
   ios_base::sync_with_stdio(false);
   cin.tie(0);
   cout.tie(0);
   
   int t = 1;
   cin >> t;

   while (t--) {
      read();
      solve();
   }

   return 0;
}

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