Submission #315134

#	Time	Username	Problem	Language	Result	Execution time	Memory
315134		2qbingxuan	Cat (info1cup19_cat)	C++14	0 / 100	1094 ms	1280 KiB

cat

#include <bits/stdc++.h>
#ifdef local
#define debug(args...) qqbx(#args, args)
template <typename ...T> void qqbx(const char *s, T ...args) {
    int cnt = sizeof...(T);
    (std::cerr << "(" << s << ") = (" , ... , (std::cerr << args << (--cnt ? ", " : ")\n")));
}
#else
#define debug(...) ((void)0)
#endif // local
#define pb emplace_back
#define all(v) begin(v), end(v)
using namespace std;
using ll = long long;

void solve() {
    int n;
    cin >> n;
    vector<int> p(n);
    for(int i = 0; i < n; i++) cin >> p[i], --p[i];
    for(int i = 0; i < n; i++) if(p[i] + p[n-1-i] != n-1) return cout << -1 << '\n', void();
    int H = n/2;
    vector<int> pos(H);
    for(int i = 0; i < n; i++) if(p[i] < H) pos[p[i]] = i;
    vector<pair<int,int>> ans;
    for(int i = 0; i < H; i++) {
        if(p[i] != i) {
            int j = pos[i];
            if(i+j == n-1)
                continue;
            /* if(p[i] >= H && j >= H) */
            /*     j = n-1-j; */
            swap(pos[p[i] < H ? p[i] : n-1-p[i]], pos[p[j] < H ? p[j] : n-1-p[j]]);
            swap(p[i], p[j]);
            swap(p[n-1-i], p[n-1-j]);
            ans.pb(i, j);
        }
        for(int j = 0; j < n; j++) cerr << p[j]+1 << (j+1==n ? '\n' : ' ');
    }
    vector<int> tmp;
    for(int i = 0; i < H; i++) if(p[i] != i) tmp.pb(i);
    if(tmp.size() % 2 == 1) return cout << -1 << '\n', void();
    debug(tmp.size());
    for(int i = 0; i < int(tmp.size()); i += 2) {
        {
            int a = n-1-tmp[i];
            int b = tmp[i+1];
            swap(p[a], p[b]);
            swap(p[n-1-a], p[n-1-b]);
            ans.pb(a, b);
        }
        {
            int a = tmp[i];
            int b = tmp[i+1];
            swap(p[a], p[b]);
            swap(p[n-1-a], p[n-1-b]);
            ans.pb(a, b);
        }
    }
    for(int j = 0; j < n; j++) cerr << p[j]+1 << (j+1==n ? '\n' : ' ');
    if(!is_sorted(all(p))) return cout << -1 << '\n', void();
    debug(ans.size());
    cout << ans.size() << ' ' << ans.size() << '\n';
    for(auto [a, b]: ans) cout << a+1 << ' ' << b+1 << '\n';
}
signed main() {
    ios_base::sync_with_stdio(0), cin.tie(0);
    int t;
    cin >> t;
    while(t--) solve();
}

Compilation message (stderr)

cat.cpp: In function 'void solve()':
cat.cpp:64:14: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   64 |     for(auto [a, b]: ans) cout << a+1 << ' ' << b+1 << '\n';
      |              ^

• Subtask 1: 0 / 15
• Subtask 2: 0 / 10
• Subtask 3: 0 / 25
• Subtask 4: 0 / 15
• Subtask 5: 0 / 35