Reduced memory usage by 50%

README.md

@@ -11,11 +11,11 @@ memory, to serve as a buffer for storing results.
 
 1. Make benchmarks.
 2. Introduce more tests.
-	2.1. Tests with pre, post and infix strings shared between the strings
-	2.2 Tests where the length of the strings are combinations of odd and
-	    even.
-3. Reduce the size of the buffer. When this was done with the old version,
-   performance was increased 100%.
+    2.1 Tests with pre, post and infix strings shared between the strings
+    2.2 Tests where the length of the strings are combinations of odd and
+        even.
+3. ~~Reduce the size of the buffer. When this was done with the old version,
+   performance was increased 100%.~~
 4. Look into SIMD instructions
 5. Look into parallelism.
 6. Templating the code

src/iosifovitch.cpp

@@ -16,26 +16,25 @@ auto levenshtein_distance(std::string_view const& a, std::string_view const& b)
 	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];
+	auto buffer = new unsigned int[buffer_length];
 
-	unsigned int * buffer[2] = {buffers, buffers + buffer_length};
-	std::iota(buffer[0], buffer[1], 0);
-	std::fill(buffer[1], buffer[1] + buffer_length, 0);
+	std::iota(buffer, buffer + buffer_length, 0);
 
 	for (auto i = 0u; i < b.size(); ++i)
 	{
-		buffer[1][0] = i + 1;
+		buffer[0] = i;
+		auto temp = i;
 		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
+			temp = std::min(
+				temp + (a[j] == b[i] ? 0u : 1u),
+				std::min(buffer[j + 1], buffer[j]) + 1u
 			);
+			std::swap(buffer[j + 1], temp);
 		}
-		std::swap(buffer[0], buffer[1]);
 	}
 
-	auto cost = buffer[0][buffer_length - 1];
-	delete [] buffers;
+	auto cost = buffer[buffer_length - 1];
+	delete [] buffer;
 	return cost;
 }