Incorrect output for larger test cases

I am trying to solve this problem : https://icpc.kattis.com/problems/different

Here’s my code :

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
int main (void)
{
    unsigned long long int x, y, z;
    while (scanf("%llu%llu", &x, &y) != EOF)
    {
        printf ("%llu\n", abs (x - y) );
        if (scanf ("%llu%llu", &x, &y) == EOF)
        break;
        printf ("%llu\n", abs (x - y) );
    }

    return 0;
}  

It gives correct output for smaller test cases but fails for the larger ones. I am using GCC 4.8.1 on Windows XP 32 BIT Edition.

Input :

1 2
232 23
23 3
456 6
4 566
45 5
45 5
666 4
34 4343
34 34
34 5646
5645 32423
23423 32423
0 5
65 0
10 12
1871293781758123 72784
1 9223372036854775807

Output :

1
209
20
450
562
40
40
662
4309
0
5612
26778
9000
5
65
2
1994345381
2

AFAIK unsigned long long int should be enough for handling 20 digit integers.

Also, is there a way for generating large number of test cases to test my code instead of manually typing them?

1 Like

First of all you don’t have to use unsigned long long. Since, long long is enough to handle 2^63 -1.

Here, is the correct


[1] but little differnt one.

For test cases. Yes, you can write a program for it like this.

    #include <stdio.h>
    int main(){
        long long i,j;
       for(i = 1,j = 100000;i<50000000;i+= 50,j+=23)
        printf("%lld %lld\n",i,j);
       return 0;
    }

By changing the values you can generate as many test cases you want.



  [1]: http://ideone.com/OLGNHy
1 Like

The problem, I think, is the abs function.

I believe abs function takes an int argument and returns an int. Now, int is a 32-bit signed data type. Naturally, only the lower-order 32 bits of an argument will get passed to the function. So, you lose some bits here.

Something similar might be happening, when the returned value is converted to long long (because of the %lld format specifier).

PS: I am not at all sure about these. But, apart from these, your code looks fine!

1 Like

Thanks for the test-case generator code. I understand your solution but I want to know what’s wrong with my code.

I changed the variable type to long long int and also changed the identifier accordingly but it still doesn’t work. http://ideone.com/08k1qo