Java noobness

Woden · 18 Jul 2012 at 18:09

I am running through the problems on Project Euler and, rather stupidly, got stuck on problem 2!

The way I am reading it is basically the sum of all the even numbers in the fibbonaci sequence under 4000000. My program runs fine, but the answer is wrong. Any pointers? Not answers please, just an idea where I went wrong

Code:

package euler_2;

/**
 * By considering the terms in the Fibonacci sequence whose values do not 
 * exceed four million, find the sum of the even-valued terms.
 * 
 * @author Woden
 */
public class Euler_2 {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        int max = 4000000; // Upper limit of the exercise
        int prev = 1; // Previous number int he sequence
        int cur = 2; // Current number in the sequence
        int next = 3; // next number in the sequence
        int sum = 0; // Sum of even terms
        
        while(prev + cur <= max) {
            if(cur % 2 == 0) {
                sum = sum + cur;
            }
            prev = cur;
            cur = next;
            next = prev + cur;
        }
        System.out.println(sum);
    }
}

orderoftheflame · 18 Jul 2012 at 19:42

int prev = 1; // Previous number int he sequence
int cur = 2; // Current number in the sequence
int next = 3; // next number in the sequence

You're starting with a current value of 2, not 1.

I like this idea, think I'll sign up and give it a go.

Woden · 18 Jul 2012 at 19:45

orderoftheflame said:
You're starting with a current value of 2, not 1.

I like this idea, think I'll sign up and give it a go.

I passed A level maths fine and I get the simplist of sequences wrong! Doh!

andshrew · 18 Jul 2012 at 19:45

I'd take a look at your while condition again as I believe that is at fault.

orderoftheflame · 18 Jul 2012 at 20:02

andshrew said:
I'd take a look at your while condition again as I believe that is at fault.

I think you could be right as well.

If you're still stuck OP, this got the right answer for me.

Code:

package co.ootf.euler;

/**
 * Created by IntelliJ IDEA.
 * User: Ben
 * Date: 18/07/12
 * Time: 19:47
 * To change this template use File | Settings | File Templates.
 */
public class Euler2 {
    
    private static final int MAX = 4000000;
    
    public static void main(String[] args) {
        int current = 1;
        int next = 2;
        int runningTotal = 0;

        while (current <= MAX ) {
            if (current % 2 == 0) {
                System.out.println("*" + current);
                runningTotal += current;
            } else {
                System.out.println(current);
            }
            int tempNext = current + next;
            current = next;
            next = tempNext;
        }

        System.out.println("total = " + runningTotal);

        
    }

}

Woden · 18 Jul 2012 at 20:41

I found it, fixed the while condition.

Thankyee

InertProtocol · 18 Jul 2012 at 21:20

Wow that's some tough questions. Kudos to those who can do them!.

uniQ · 18 Jul 2012 at 21:24

Woop just checked my Java dropbox and still have my Project Euler folder, completely forgot about this. Only got to the 4th Proj with Java. Got a bit further with PHP but don't seem to have any backups

Will definitely pick it back up again w/ Java thanks for the reminder

Dj_Jestar · 19 Jul 2012 at 16:51

Damn you and damn this thread.

*goes back to euler problem solving*