Category Archives: Programming

Stalin-Sort

Programming, , , , ,

I just love this idea:

I came up with a single pass O(n) sort algorithm I call Stalin-Sort. U iterate down the list of elements checking if they are in order. Any element which is out of order is eliminated. At the end u have a sorted list

But when you have an input such as [42,1,2,3,4,5,6] you just get
[42] instead of [1,2,3,4,5,6]. You can get a better
result if you use divide and conquer. And that is something Stalin
would do, don’t you think? So I implemented a recursive solution in
Java. It tries all possible results, which is not a single pass and therefore
defeats the purpose of having a fast O(n) algorithm. And my implementation isn’t even in-place. A new data structure has to be created. That’s why I also added an
implementation using a linked list, which is what Mathew describes.

The code is on pastebin: https://pastebin.com/rEmvZSiA

Recursive FizzBuzz

Java, Java Interview Questions, Programming, , , , , 
import static java.lang.System.out;

Simple two-liner:

static void f(int a, int z) {
	out.println(a % 15 < 1 ? "FizzBuzz" : a % 3 < 1 ? "Fizz" : a % 5 < 1 ? "Buzz" : a);
	if (a < z) f(1 + a, z);
}

Without using the literal “FizzBuzz”:

static void g(int a, int z) {
  int x = 0;
  if (a % 3 < 1) { out.print("Fizz"); ++x; }
  if (a % 5 < 1) { out.print("Buzz"); ++x; }
  if (x < 1) out.print(a);
  out.println();
  if (a < z) g(1 + a, z);
}

Note that I use x<1 instead of x==0 to save a single character.

Y Combinator in Java 8

Java, Programming, , , , , ,

The Y Combinator allows us to use recursion without actually using the recursion that Java already has. And Java 8 actually doesn’t support recursion in lambdas. So this is one way of solving the problem. The simpler one would be to use a recursive Java method and then use a method reference to it (as in MyMathsFunctions::factorial). This is to show that Curry was right and we can do it with nothing but lambda expressions. Since Java is strongly typed I also need an interface, which references itself in the type declaration. This is necessary because at some point we need to apply a function to itself.

There are enough wiki and blog pages and articles on this. Even videos. So I won’t explain it in details. It’s nothing new, just written in Java 8.

	private static <T> T apply(UnaryOperator<UnaryOperator<T>> fn, T arg) {
		return ((Function<UnaryOperator<UnaryOperator<T>>, UnaryOperator<T>>)
				a -> ((Fn2Op<T>) b -> b.apply(b))
				.apply(
					c -> a.apply(
						x -> c.apply(c).apply(x)
					)
				)).apply(fn).apply(arg);
	}

Code on Pastebin

The full Code is here: https://pastebin.com/M2RmRqdU

Encapsulation

Java, Misconceptions, Programming, , , , , ,

In my blog I write about misconceptions. Encapsulation is something you learn when you study Java and OOP. But it seems that most books fail to truly explain the problems you want to solve with it and those you get by using it. Often it’s just a short chapter or even just a small part about the important concepts of OOP. This is leading to misconceptions and poor understanding of OOP.

(Note: I wrote this before the release of Java 10. Expect that some things are somewhat outdated.)

Continue reading Encapsulation →