Tag Archives: recursive

Recursive FizzBuzz

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);
  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

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))
					c -> a.apply(
						x -> c.apply(c).apply(x)

Code on Pastebin

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

Fork/Join with non-recursive Task

Most tutorials use some recursive Task to calculate a Fibonacci number or something similar. This leads to the false impression that Fork/Join can only handle recursive Tasks (e.g. Divide-And-Conquer). Here’s a very simple example of a non-recursive Task.
Continue reading Fork/Join with non-recursive Task