Question

I have written a small piece of code that would perform Run length encoding kind of stuff on 1-D array but still far from desired result.

main()
{
    int a[8]={2,0,0,0,3,0,0,9};
    int i,temp,ct=0,flag,m;
    int found[90]={0};
    for(i=0;i<=7;i++)
    {
        if(!a[i])
        {
            ct++;
            if(!found[a[i]])
            {
                flag=i;
                found[a[i]]=1;
            } 
        } 
    }

    a[flag]=ct;
    m=ct;    
    for(i=0;i<m;i++)
    {
        printf("%d",a[i]);
    }       
}/* end of main*/

Now for above array i would like to have output something below

 2 5 0 3 9

But with my piece of code am getting

 2 5 0 0 3

Can I have any suggestion on that?

Answer 1

Shouldn’t run length encoding turn 2,0,0,0,3,0,0,9 into 2 1 0 3 3 1 2 0 9 1?

1) The first thing I see is wrong is that you aren’t looking at the entire array. You’re using < to stop before 8, but also stopping at 7, so you only evaluate array items 0 – 6.

2) If ct stands for count it’s never reset (ct=0 only on declaration). Also it’s assignment is this: a[flag]= ct; which overwrites your original data. It basically tracks the value of i.

This is my version I’ve just put together:

#define SZ 8

main()
{
    int a[SZ]={2,0,0,0,3,0,0,9};
    int i; //absolute position

    int runningCount = 1; //because we start at array index 1 and not zero

    for (i = 1; i <= SZ; i++) {
        if (a[i - 1] == a[i]) //value same as one before it...
           runningCount++;
        else { // new value found. print last one, and the count of the last one.
            printf("%d %d ", a[i - 1], runningCount);
            runningCount = 1; //reset for next loop
        }
    }

    return 0;
}

The output is 2 1 0 3 3 1 0 2 9 1

Ok based on the comment left below, your algorithm would actually look like this:

#define SZ 8

main()
{
    int a[SZ]={2,0,0,0,3,0,0,9};
    int i; //absolute position

    int zero_count = 0; //target zeros specifically...

    for (i = 0; i < SZ; i++) {
        if (a[i] == 0)
           zero_count++;
    }

    //now write it out in a bizarre, unparsable format again...

    for (i = 0; i < SZ; i++) {

        if (a[i] != 0)           //write out all non zero values
            printf("%d ", a[i]);

        if (i == 0) { //this says put the zero count after the first number was printed
           printf("%d 0 ", zero_count); //inserting it into a strange place in the array
        }

    }

    return 0;
}

which outputs: 2 5 0 3 9