#include <iostream>
#include <vector>
 
using namespace std;
 
auto pairs(const vector<int>& in, int groupLength = 4) {
	vector<pair<int, int>> result;
	int groups = in.size() / groupLength;
	for (int group = 0; group < groups; ++group) {
		int i = group * groupLength;
		int j = i + groupLength - 1;
		while (i < j) {
			result.emplace_back(in[i++], in[j--]);
		}
	}
	return result;
}
 
int main() {
	vector<int> test = {1,2,3,4,5,6,7,8};
	for (auto p : pairs(test)) {
		cout << p.first << ' ' << p.second << endl;
	}
	return 0;
}

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