CODEWITHSUNDEEP
javaalgorithmmathfibonacci
Jonatan Mattsson
Jonatan Mattsson

Reputation: 11

Creating a Fibonacci sequence, finding sum of all odd numbers

I am trying to create a Fibonacci sequence, starting with 1 and 2, that ends at 1000. That part I have figured out, but it also needs to return the sum of all odd numbers. I thought I figured it out, but I keep getting results that are incorrect.

Here is my code, appreciate any help I can get.

public class Fibonacci {
    public static void main(String[] args) {
        int n = 1000, t1 = 1, t2 = 2, odd = 0;
        
        System.out.print("Fibonacci to " + n + ": ");
        while (t1 <= n)
        {
            System.out.print(t1 + " + ");

            int sum = t1 + t2;
            t1 = t2;
            t2 = sum;
            if (t1 % 2 != 0)
                odd = odd + t1;
        }
        System.out.print("All odd numbers combined are: " + odd);
    }
}

Upvotes: 1

Views: 469

Answers (2)

Paul
Paul

Reputation: 1150

Since I see that someone else provided a decent answer, I enjoyed cooking up something else using List<>, Streams and recursion. You said that you're fairly new to programming, so don't hesitate to ask what's going on in my code. Although I learned mostly by googling myself.

public class Fibonacci {

    private static final List<Integer> oddNumbers = new ArrayList<>();

    public static void main(String[] args) {

        generateFibonacciSequence(1000).forEach(number -> {
            if (number < 1000){
                System.out.println(number);

                if (number % 2 != 0){
                    oddNumbers.add(number);
                }
            }
        });
        System.out.println("sum of odd numbers = " + oddNumbers.stream().mapToInt(oddNumber -> oddNumber).sum());
    }

    public static IntStream generateFibonacciSequence(int limit) {
        AtomicInteger number = new AtomicInteger(0);
        return IntStream.generate(
                () -> fibonacci(number.incrementAndGet()))
                .takeWhile((numberValue -> numberValue < limit));
    }

    private static int fibonacci(int position) {
        if (position == 1 || position == 2) {
            return 1;
        }
        return fibonacci(position - 2) + fibonacci(position - 1); //recursion
    }
}

Upvotes: 0

Daniel
Daniel

Reputation: 7724

You are skipping values in your algorithm.

Before you add the current t1 value into odd, you update it to the next.

The fibonacci sequece is:

t1  t2  t1  t2  t1  t2   t1   t2
1   2   3   5   8   13   21   34

Instead of adding 1, you are updating t1 to 3 before, so 1 is ignored.

Inside your while loop, try this:

System.out.print(t1 + " + ");

if (t1 % 2 != 0) odd += t1;
t2 += t1;
t1 = t2 - t1;

Upvotes: 2

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