Add 'longest_subsequence.cpp'

longest_subsequence.cpp

@@ -0,0 +1,55 @@
+
+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);
+}