Codeforces Round #217 (Div. 2) / 370C Mittens (构造&贪心)

http://codeforces.com/contest/370/problem/C

/*31ms,0KB*/

#include<iostream>
#include<algorithm>
using namespace std;

int C[5005];

int main()
{
	int N, M;
	cin >> N >> M;
	for (int i = 0; i < N; i++) cin >> C[i];
	sort(C, C + N);
	int cnt = 0;
	for (int i = 0; i < N; i++) cnt += (C[i] != C[(i + N / 2) % N]);
	cout << cnt << endl;
	for (int i = 0; i < N; i++) cout << C[i] << ' ' << C[(i + N / 2) % N] << endl;
	return 0;
}