#include "iosifovitch.h"
#include <numeric>

auto levenshtein_distance(std::string_view const& a, std::string_view const& b) -> unsigned int {
	if (a.size() == 0 || b.size() == 0) return a.size() + b.size();

	if (a.size() > b.size()) return levenshtein_distance(b, a);

	auto i = 0u;
	while (i < a.size() && a[i] == b[i]) ++i;

	if (i != 0) return levenshtein_distance(a.substr(i), b.substr(i));

	i = 0;
	while (i && a[a.size() - i] == b[b.size() - i]) ++i;
	if (i != 0) return levenshtein_distance(a.substr(0, a.size() - i), b.substr(0, b.size() - i));

	auto const buffer_length = a.size() + 1;
	auto buffers = new unsigned int[buffer_length * 2];

	unsigned int * buffer[2] = {buffers, buffers + buffer_length};
	std::iota(buffer[0], buffer[1], 0);
	std::fill(buffer[1], buffer[1] + buffer_length, 0);

	for (auto i = 0u; i < b.size(); ++i)
	{
		buffer[1][0] = i + 1;
		for (auto j = 0u; j < a.size(); ++j)
		{
			buffer[1][j + 1] = std::min(
				buffer[0][j] + (a[j] == b[i] ? 0u : 1u),
				std::min(buffer[0][j + 1], buffer[1][j]) + 1u
			);
		}
		std::swap(buffer[0], buffer[1]);
	}

	auto cost = buffer[0][buffer_length - 1];
	delete [] buffers;
	return cost;
}