The challenge
You’re going to provide a needy programmer a utility method that generates an infinite sized, sequential IntStream which contains all the numbers in a fibonacci sequence.
A fibonacci sequence starts with two 1s. Every element afterwards is the sum of the two previous elements. See:
1, 1, 2, 3, 5, 8, 13, ..., 89, 144, 233, 377, ...
The solution in Java code
Option 1:
import java.util.function.IntSupplier;
import java.util.stream.IntStream;
public class Utility {
public static IntStream generateFibonacciSequence() {
return IntStream.generate(new IntSupplier() {
int a = 0;
int b = 1;
@Override
public int getAsInt() {
int x = a + b;
a = b;
b = x;
return a;
}
});
}
}
Option 2:
import java.util.stream.Stream;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.IntStream;
public class Utility {
public static IntStream generateFibonacciSequence() {
return Stream.iterate(new Integer[]{1, 1}, p -> new Integer[]{p[1], p[0] + p[1]})
.mapToInt(integers -> integers[0]);
}
}
Option 3:
import java.util.stream.IntStream;
import java.util.stream.Stream;
import java.util.concurrent.atomic.AtomicInteger;
public class Utility {
public static IntStream generateFibonacciSequence() {
AtomicInteger fibonacci = new AtomicInteger(1);
return IntStream.iterate(1, x -> fibonacci.getAndAdd(x));
}
}
Test cases to validate our solution
import org.junit.Test;
import java.util.PrimitiveIterator;
import static org.junit.Assert.assertArrayEquals;
import static org.junit.Assert.fail;
public class TestSuite {
@Test
public void testThatTheFirstTwentyElementsAreCorrect() {
assertArrayEquals("The first twenty elements are incorrect!",
new int[] {1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765},
Utility.generateFibonacciSequence().limit(20).toArray());
}
@Test(timeout = 30)
public void testRecursivePropertyInStreamByRandomLeaps() {
for (int i = 0; i < 3; i++) { // Repeat three times
final PrimitiveIterator.OfInt iterator =
Utility.generateFibonacciSequence()
.skip((int) (Math.random() * 900)) // Begin leap
.limit(20) // End leap
.iterator();
int previous = iterator.nextInt(),
current = iterator.nextInt();
while (iterator.hasNext()) {
final int next = iterator.next();
if (next != previous + current)
fail(String.format("Elements %s, %s are followed by %s!", previous, current, next));
previous = current;
current = next;
}
}
}
}
