PublicBin/longest_subsequence.cpp

auto subsequence_boundary(auto start, auto end,auto pred) {
	using live_iterator = decltype(start);
	using distance_t = std::invoke_result_t<decltype(std::distance<live_iterator>), live_iterator, decltype(end)>;
	distance_t distance = std::distance(start, end);
	
	if(distance < 1) {
		return start;
	}
	
	if(distance == 1) {
		return ++start;
	}
	
	live_iterator next = start;
	++next;
	
	while(not pred(*start, *next)) {
		++start;
		++next;
		if(next == end) return next;
	}
	
	return next;
}

auto longest_matching_subsequence(auto start, auto end, auto pred) {
	using live_iterator = decltype(start);
	using distance_t = std::invoke_result_t<decltype(std::distance<live_iterator>), live_iterator, decltype(end)>;
	live_iterator current = start;
	struct {
		live_iterator best_s;
		live_iterator best_e;
	} results;
	results.best_s = start;
	results.best_e = start;
	distance_t best_length = 0;
	while(current != end) {
		live_iterator next = subsequence_boundary(current, end, pred);
		distance_t subsequence_length = std::distance(current, next);
		if(subsequence_length > best_length) {
			results.best_s = current;
			results.best_e = next;
			best_length = subsequence_length;
		}
		current = next;
	}
	return results;
}

TEST_CASE("Subsequence") {
	std::vector<int> list = {0,1,2,3,4,5,0,1,0,2,5,8,7};
	auto [s,e] = longest_matching_subsequence(list.begin(), list.end(), std::greater<int>{});
	REQUIRE(std::distance(s,e) == 6);
}