Submission #775172

#	Time	Username	Problem	Language	Result	Execution time	Memory
775172		daoquanglinh2007	Xor Sort (eJOI20_xorsort)	C++17	65 / 100	6 ms	1100 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(){
	for (int i = N; i >= 1; i--){
		int k = 1;
		for (int j = 2; j <= i; j++)
			if (a[j] > a[k]) k = j;
		if (k == i) continue;
		int cur = a[i];
		bool ok = 0;
		for (int j = i+1; j <= N; j++){
			cur ^= a[j];
			if (cur < a[i+1] && cur >= a[k]){
				ok = 1;
				for (int ii = j-1; ii >= i; ii--)
					op(ii, ii+1);
				for (int ii = i+1; ii < j; ii++)
					op(ii, ii+1);
				break;
			}
		}
		if (ok) continue;
		for (int j = 1; j < i; j++)
			if (a[j] > a[j+1]){
				op(j+1, j);
				op(j, j+1);
				op(j+1, j);
			}
	}
}

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:80:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   80 |  for (int i = 0; i < ans.size(); i++)
      |                  ~~^~~~~~~~~~~~

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