CODEWITHSUNDEEP
c
Chris Browne
Chris Browne

Reputation: 1612

Collatz Conjecture code "bouncing" between 13 and 19

I'm trying to solve problem 14 on project euler, and my initial brute force attempt has me stumped. For some reason, the code encounters a cycle between 13 and 19. I don't think I can righteously proceed onto non-brute methods unless I can first get the brute-force method to at least compute correctly. My code looks like this:

unsigned int loop(unsigned int n) 
{
    unsigned int count = 0;
    while(1) 
    {
        while(is_even(n)) 
        {
            n /= 2;
        }
        if(n > 1)
            n = (n * 3) + 1;
        else
            break;
        count++;
        printf("%d,", n);
    }
    printf("%d\n", n);
    return count;
}

is_even(n) is computed as "n & 0x01".

Can anyone tell me why the output is a continuous (and theoretically endless) stream of "13,19," repeated?

Upvotes: 0

Views: 400

Answers (1)

icktoofay
icktoofay

Reputation: 129149

n & 0x01 will be 1 if n is odd, not if it is even. Change is_even to return !(n & 0x01).

Upvotes: 3

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