#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
#include <list>
#include <algorithm>
#include <iterator>
using namespace std;

list<int> f(list<int>::size_type i);
list<int> permute(list<int>::size_type i);

/*
Output a random permutation of the integers 0 to n-1 inclusive.
Each pair of numbers falls in the same line.
*/

const int n = 20 / 2;	//number of pairs of chars per line

int main()
{
	srand(time(0));
	const list<int> li = f(12);
	copy(li.begin(), li.end(), ostream_iterator<int>(cout, "\n"));
	return EXIT_SUCCESS;
}

list<int> f(list<int>::size_type i)	//i is number of lines
{
	if (i <= 0) {
		return list<int>(i);
	}

	list<int> li = f(i - 1); 
	const list<int> p = permute(n); 

	for (list<int>::const_iterator it = p.begin(); it != p.end(); ++it){
		list<int>::iterator in = li.begin();
		list<int>::size_type r = rand() % (li.size() + 1);
		if (r % 2 != 0) {
			--r;
		}
		advance(in, r);
		li.insert(in, *it + n * (i - 1));
		++it;
		li.insert(in, *it + n * (i - 1));
	}

	return li;
}

list<int> permute(list<int>::size_type i)
{
	if (i <= 1) {
		return list<int>(i);
	}

	list<int> li = permute(i - 1); 
	list<int>::iterator it = li.begin();
	advance(it, rand() % i);
	li.insert(it, i - 1);
	return li;
}