Submission #315146

#	Time	Username	Problem	Language	Result	Execution time	Memory
315146		Kevin_Zhang_TW	Cat (info1cup19_cat)	C++17	0 / 100	22 ms	640 KiB

cat

#include<bits/stdc++.h>
#define pb emplace_back
#define AI(i) begin(i), end(i)
using namespace std;
using ll = long long;
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void debug(auto L, auto R) { while (L < R) cerr << *L << " \n"[L+1==R], ++L; }
void kout(){ cerr << endl; }
template<class T1, class ...T2> void kout(T1 a, T2 ...e) { cerr << a << ' ', kout(e...); }
#else
#define DE(...) 0
#define debug(...) 0
#endif
const int MAX_N = 3000010;
int per[MAX_N], n, pos[MAX_N];
void fail() {
	puts("-1"), exit(0);
}
void sw(int a, int b) {
	DE(a, b, per[a], per[b]);
	swap(per[a], per[b]);
	swap(pos[per[a]], pos[per[b]]);
}
void solve() {
	cin >> n;
	for (int i = 1;i <= n;++i)
		cin >> per[i], pos[per[i]] = i;
	for (int i = 1;i <= n/2;++i)
		if (per[i] > n/2) fail();
	vector< pair<int,int> > res;
	res.reserve(n);
	int m = n / 2;

	DE(m);
	for (int i = 1;i <= m;++i) {
		while (i != per[i]) {
			int x = per[i];
			res.pb(i, pos[i]);
			int a = i, b = pos[i], c = n-a+1, d = n-b+1;

			sw(a, b);
			sw(c, d);
		}
	}
	debug(per+1, per+1+n);
	for (int i = 1;i <= n;++i)
		if (i != per[i]) {
			cout << -1 << '\n';
			return;
		}

	cout << res.size() << '\n';
	for (auto [a, b] : res)
		cout << a << ' ' << b << '\n';

}
signed main(){
	ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	int T;
	cin >> T;
	while (T--)
		solve();
}

Compilation message (stderr)

cat.cpp: In function 'void sw(int, int)':
cat.cpp:12:17: warning: statement has no effect [-Wunused-value]
   12 | #define DE(...) 0
      |                 ^
cat.cpp:21:2: note: in expansion of macro 'DE'
   21 |  DE(a, b, per[a], per[b]);
      |  ^~
cat.cpp: In function 'void solve()':
cat.cpp:12:17: warning: statement has no effect [-Wunused-value]
   12 | #define DE(...) 0
      |                 ^
cat.cpp:35:2: note: in expansion of macro 'DE'
   35 |  DE(m);
      |  ^~
cat.cpp:38:8: warning: unused variable 'x' [-Wunused-variable]
   38 |    int x = per[i];
      |        ^
cat.cpp:13:20: warning: statement has no effect [-Wunused-value]
   13 | #define debug(...) 0
      |                    ^
cat.cpp:46:2: note: in expansion of macro 'debug'
   46 |  debug(per+1, per+1+n);
      |  ^~~~~

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