Thread: 3n+1 problem

If you don't know this problem it is here http://acm.uva.es/p/v1/100.html.
I don't know why my code is receiving wrong answer. It is right for the selected input. Also, I've done 1 1000000 and it doesn't seg fault on any numbers. Then I thought from the way that they worded it that they could give input out of order (swap function), but that didn't fix it. Why do they say it is wrong.

Code:

/*@JUDGE_ID:   110101   100 C "3n+1"*/

#include <stdio.h>

unsigned long int func(unsigned long int num);
void swap(unsigned long int *tx,unsigned long int *ty);

int main(void){
        unsigned long x,y,z,max=0,temp;
        fflush(stdout);
        while(scanf("&#37;lu %lu", &x,&y)==2){
                if(x>y) swap(&x,&y);
                max = 0;
                for(z=x;z<=y;z++){
                        temp = func(z);
                        if(temp>max) max = temp;
                }
                printf("%lu %lu %lu\n",x,y,max);
        }
        return 0;
}
void swap(unsigned long int *tx,unsigned long int *ty){
        unsigned long int temp;
        temp = *tx;
        *tx = *ty;
        *ty = temp;
}
unsigned long int func(unsigned long int num){
        if(num == 1){
                return 1;
        }
        else if(num%2==0){
                return 1 + func(num/2);
                }
        else{
                return 1 + func(num*3+1);
        }
}

Thanks

Maybe it takes too long?
Maybe it's needlessly massively recursive?
Maybe your swap function truncates data?

Code:

        else if(num%2==0){
                return 1 + func(num/2);
                }
        else{
                return 1 + func(num*3+1);

Why do you add 1?

Also, you're not supossed to use recursion.

Look at this, it's working:

Code:

int main()
{
        int n;
        start: scanf("%d",&n);
        print: printf("%d\n",n);
        if(n==1) goto start;
        if(n%2==1)
            n = 3*n + 1;
        else
            n = n/2;

        goto print;

        return 0;
}

You're swap function is algo wrong, because you assing a long int to an int, maybe in some architectures that'll work fine but it's not portable.

Currently, I can't see anything wrong with it, but some sample output would be of some assisstance.

The integers i and j must appear in the output in the same order in which they appeared in the input

Consider an input of 1000 900.