Submission #775081

#	Time	Username	Problem	Language	Result	Execution time	Memory
775081		daoquanglinh2007	Xor Sort (eJOI20_xorsort)	C++17	65 / 100	7 ms	1236 KiB

xorsort

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

#define pii pair <int, int>
#define fi first
#define se second
#define mp make_pair
#define getbit(x, i) ((x&(1<<i)) != 0)

const int NM = 1000;

int N, S, a[NM+5];
vector <pii> ans;

void op(int i, int j){
	ans.push_back(mp(i, j));
	a[i] ^= a[j];
}

void solve1(){
	bool back = 0;
	while (true){
		bool ok = 1;
		if (!back){
			for (int i = 1; i < N; i++)
				if (a[i] > a[i+1]){
					ok = 0;
					op(i+1, i);
					op(i, i+1);
					op(i+1, i);
				}
		}
		else{
			for (int i = N-1; i >= 1; i--)
				if (a[i] > a[i+1]){
					ok = 0;
					op(i+1, i);
					op(i, i+1);
					op(i+1, i);
				}
		}
		if (ok) break;
		back = !back;
	}
}

void solve2(){
	int tar = N+1;
	for (int i = 19; i >= 0; i--){
		bool ok = 0;
		for (int j = 1; j <= N; j++)
			if (getbit(a[j], i)){
				ok = 1;
				break;
			}
		if (ok == 0) continue;
		tar--;
		for (int j = 1; j < tar; j++)
			if (getbit(a[j], i) && !getbit(a[j+1], i)){
				op(j+1, j);
				op(j, j+1);
			}
			else if (getbit(a[j], i) && getbit(a[j+1], i)){
				op(j, j+1);
			}
	}
}

int main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin >> N >> S;
	for (int i = 1; i <= N; i++) cin >> a[i];
	if (S == 1) solve1();
	else solve2();
	cout << ans.size() << '\n';
	for (int i = 0; i < ans.size(); i++)
		cout << ans[i].fi << ' ' << ans[i].se << '\n';
	return 0;
}

Compilation message (stderr)

xorsort.cpp: In function 'int main()':
xorsort.cpp:78:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   78 |  for (int i = 0; i < ans.size(); i++)
      |                  ~~^~~~~~~~~~~~

• Subtask 1: 25 / 25
• Subtask 2: 0 / 35
• Subtask 3: 40 / 40