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#include <iostream>
#include <set>
#include <array>
#include <algorithm>
#include <vector>
using namespace std;
 
const size_t N = 8;
typedef array<size_t, N> perm;
typedef set<perm> perms;
 
perms s;
 
void init (perms& s) {
	s.clear();
	perm ta;
	for (size_t i = 0; i < N; ++i) ta[i] = i;
	s.insert(ta);
	while(next_permutation(ta.begin(), ta.end()))
		s.insert(ta);
}
 
size_t sieve (perms& s, pair<size_t, size_t> p) {
	vector<perm> for_insert;
	vector<perms::iterator> for_erase;
 
	for (auto sit = s.begin(); sit != s.end(); ++sit) {
		if ((*sit)[p.first] > (*sit)[p.second]) {
			for_erase.push_back(sit);
			for_insert.push_back(*sit);
			swap(for_insert.back()[p.first], for_insert.back()[p.second]);
		}
	}
 
	for (auto& eit: for_erase)
		s.erase(eit);
 
	for (auto& a: for_insert) {
		bool t = s.insert(a).second;
		//if (t) cout << "INSERT!" << endl;		
	}
 
	return s.size();
}
 
void show (const perms& s) {
	cout << s.size() <<  " total:" << endl;
	for (auto& a: s) {
		for (auto& e: a) cout << e;
		cout << endl;
	}
}
 
int main() {
	init(s);
	cout << s.size() << endl;
 
	cout << sieve(s, {0, 4}) << endl;
	cout << sieve(s, {0, 3}) << endl;
	cout << sieve(s, {2, 7}) << endl;
	cout << sieve(s, {6, 1}) << endl;
	cout << sieve(s, {4, 3}) << endl;
	cout << sieve(s, {6, 5}) << endl;
	cout << sieve(s, {0, 1}) << endl;
 
 
	show(s);
 
    return 0;
}

Success #stdin #stdout 0.05s 10128KB

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