Question

I have a large string char myStr=”AAAABBBCCCCCCDDDEFGHHIJJ”.
I shall pass this string to my string compressing function which should return me the string in below format myStr =”A4B3C6D3EFGH2IJ2″
Also, the new string replacements should happen in the same passed string only. One cannot create a temp array.

Below is my func and am not able to figure out the deletion of duplicates and replacing with its count in the same string.

 #include<stdio.h>
 #include<string.h>


 char* StrCompress(char myStr[])
 {
char *s = myStr;
int len = strlen(myStr);
char *in = myStr;
int count =0;
int i=0;


while(*(s) != '\0')
{
    if(*(s)==*(s+1))
    {
        count++;

        if(count == 1)
        {
            in = s;
        }
        s++;

    }
    else
    {
        //myStr[count-1]=count;
        memcpy(in+1,s+1,count);
        s=in;
        count =0;

    }
    i++;
}

return myStr;



}

int main(){

char myStr[] ="AAAABBBCCCCCEEFGIIJJJKLMNNNNOOO";

printf("Compressed String is : %s\n",StrCompress(&myStr));

return 0;

}

Answer 1

A slightly modified version:

char* StrCompress(char myStr[])
{
  char *s, *in;
  for (s = myStr, in = myStr; *s; s++) {
    int count = 1;
    in[0] = s[0]; in++;
    while (s[0] == s[1]) {
      count++;
      s++;
    }   
    if (count > 1) {
      int len = sprintf(in, "%d", count);
      in += len;
    }   
  }
  in[0] = 0;
  return myStr;
}

Additionally, you should not use the address of operator when calling with an array name:

StrCompress(myStr); // not StrCompress(&myStr)

If you are assuming that a character can’t repeat more then 9 times, then you can use in[0] = '0' + count instead of the sprintf stuff:

if (count > 1) {
  in[0] = '0' + count;
  in++;
}