Question

This is a brute force attempt to solve the problem, but it is not giving the right answer. The program runs, but its not producing desired output. I believe the logic and program is correct.

This is problem of a famous site (don’t want to a spoiler)

It asks for the number that produces the longest Collatz chain under one million.

class Euler
{

public static void main (String args[])
{
    long len,longLength=0;
    for(long i =3;i<=1000000;i++)
    {
        len = Euler14.numFucs(i);
        System.out.println("Ans"+len+"\t"+i);
        if(len>longLength)
            longLength=len;
    }
    System.out.println(longLength);
}


public static long numFucs(long num)
{
    long count=1,$test=0;
    while(num>1)
    {
        if(num%2==0)
        {
            num=num/2;

        }
        else
        {
            num=3*num+1;

        }
        count++;


    }
    //System.out.println("\tEnd");
    return count;
    }
}

Answer 1

Well, I feel like it’d be cheating to give you the code for the right answer, as a fellow Project Euler fan. You’re outputting the length of the longest chain, not the number that obtains it. If you really want, I can show you the one line that needs to change, but, honestly, this is a simple fix, and I challenge you to do it yourself.