spoj question BISHOPS. getting wrong answer. heres my code

[depster]

#include<stdio.h>
#include<string.h>
int main()
{
    char a[109];
    int i,j,b[109],x,temp,t=1024;
    while(t>0)
    {
        scanf("%s",a);
        if(strlen(a)==1 && a[0]=='1')
        {
            printf("1");
        }
        else
        {
            if(a[strlen(a)-1]!='0')
            {
                a[strlen(a)-1]=a[strlen(a)-1]-1;
            }
            else
            {
                for(j=strlen(a)-1;a[j]=='0'&&j>0;j--)
                {
                    a[j]='9';
                    if(a[j-1]!='0')
                    {
                        a[j-1]=a[j-1]-1;
                    }
                }
            }
            j=0;
            for(i=strlen(a)-1;i>=0;i--)
            {
                b[j]=a[i]-'0';
                j++;
            }
            temp=0;
            for(i=0;i<j;i++)
            {
                x=b[i]*2+temp;
                b[i]=x%10;
                temp=x/10;
            }
            while(temp>0)
            {
                b[i]=temp%10;
                temp=temp/10;
                i++;
            }
            for(j=i-1;j>=0;j--)
                printf("%d",b[j]);
        }
        printf("\n");
        t--;
    }

    return(0);

}

[Rabbit]

You need to tell us what input you're using, what answer it's giving you, and what the answer is supposed to be.

[depster]

http://www.spoj.com/problems/BISHOPS/

here is the link to the problem. I'm getting all the answers correct on my compiler and even on ideone compiler but spoj compiler shows wrong answer

[Rabbit]

I just put your code in ideone and the output is wrong. It outputs 2, 4, 2, and then a bunch of 1s. That does not match the expected output of 2, 4.

[depster]

i have modified my code but still it is showing wrong answer on spoj compiler and correct answer on ideone
earlier i was not able to detect eof but now i have corrected it. My algorithm just computes 2*(n-1) for large numbers and computes 1 for n=1. Is my algorithm correct?

#include<stdio.h>
#include<string.h>
int main()
{
    char a[109];
    int i,j,b[109],x,temp;
    while(fscanf(stdin,"%s",a)==1)
    {

        if(strlen(a)==1 && a[0]=='1')
        {
            printf("1");
        }
        else
        {
            if(a[strlen(a)-1]!='0')
            {
                a[strlen(a)-1]=a[strlen(a)-1]-1;
            }
            else
            {
                for(j=strlen(a)-1;a[j]=='0'&&j>0;j--)
                {
                    a[j]='9';
                    if(a[j-1]!='0')
                    {
                        a[j-1]=a[j-1]-1;
                    }
                }
            }
            j=0;
            for(i=strlen(a)-1;i>=0;i--)
            {
                b[j]=a[i]-'0';
                j++;
            }
            temp=0;
            for(i=0;i<j;i++)
            {
                x=b[i]*2+temp;
                b[i]=x%10;
                temp=x/10;
            }
            while(temp>0)
            {
                b[i]=temp%10;
                temp=temp/10;
                i++;
            }
            for(j=i-1;j>=0;j--)
                printf("%d",b[j]);
        }
        printf("\n");
    }
    return(0);

}

[Rabbit]

What answer is it showing on spoj?

[depster]

it just shows wrong answer

[Rabbit]

It's hard to say then. If you don't know what the output is supposed to be, then that makes it difficult to know if your algorithm is correct. The only thing you can really do is study the problem to make sure your algorithm is correct.

[donbock]

Array a holds the digit characters of the grid size. Array b starts out holding something related to the digit numbers of the grid size and ends up holding the digit numbers of the result.

You mention 2*(n-1). The times-2 takes place on numbers at lines 37-49. The subtract-1 takes place on characters at lines 16-30. It would be a lot easier to also do the subtract-1 on numbers instead of characters. Borrow and carry are especially easier. Hint: 2*(n-1) = (2*n)-2.

Things to keep in mind:

• What if the result has more digits than the input? Where will you put the extra digit(s)?
• The number array won't be null-terminated.
• Your program will crash badly if the input string contains anything other than digits. I suppose you can trust spoj not to do that to you but ...
• Your program will crash badly if the input string is longer than array a. I suppose you can trust spoj not to do that to you but ...
• You have no comments! At the very least you should state your analytical solution to the Bishops problem.