26 lines
889 B
Java
26 lines
889 B
Java
import java.util.function.Function;
|
|
|
|
@FunctionalInterface
|
|
interface SelfApplicable<OUTPUT> {
|
|
OUTPUT apply(SelfApplicable<OUTPUT> input);
|
|
}
|
|
|
|
class Utils {
|
|
public static <INPUT, OUTPUT> SelfApplicable<Function<Function<Function<INPUT, OUTPUT>, Function<INPUT, OUTPUT>>, Function<INPUT, OUTPUT>>> y() {
|
|
return y -> f -> x -> f.apply(y.apply(y).apply(f)).apply(x);
|
|
}
|
|
|
|
public static <INPUT, OUTPUT> Function<Function<Function<INPUT, OUTPUT>, Function<INPUT, OUTPUT>>, Function<INPUT, OUTPUT>> fix() {
|
|
return Utils.<INPUT, OUTPUT>y().apply(Utils.<INPUT, OUTPUT>y());
|
|
}
|
|
|
|
public static long fib(int m) {
|
|
if (m < 0)
|
|
throw new IllegalArgumentException("n can not be a negative number");
|
|
|
|
return Utils.<Integer, Long>fix().apply(
|
|
f -> n -> (n < 2) ? n : (f.apply(n - 1) + f.apply(n - 2))
|
|
).apply(m);
|
|
}
|
|
}
|