character combinations

Hello all.
I need a function that produces this strings
a , b, aa ,ab, ba ,bb ,aaa,aab, aba ,abb baa ,bab ,bba , bbb ,aaaa...
It 's NOT exactly like binary counting (in binary after bbb (111) is aaaa (1000))

char* GetNextString(char* previous)

i.e . GetNextString("bba")="bbb" , GetNextString("bbb")="aaaa"
I hope you understand what i need
Thank you !

I need a death ray. I need it to be able to wipe out entire armies and lots of buildings.

How about you give me the death ray and I give you your GetNextString() function? ;)

> It 's NOT exactly like binary counting
Close enough though.
Once you understand base 2 counting, plus I take it you already understand base 10 counting, then figuring out base 26 counting should be easy.

Quote:

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Originally Posted by Salem

> It 's NOT exactly like binary counting
Close enough though.
Once you understand base 2 counting, plus I take it you already understand base 10 counting, then figuring out base 26 counting should be easy.

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This isn't base 26, he's using only a's and b's. And like he said, it's not the same as counting, since if we just say a is 0 and b is 1, then the increasing series would be:

a, b, ba, bb, baa, bab, bba, bbb...

That's not the series he wants.

External loop is on string length
Internal - is just a binary counter from 0 to 2^k-1
for example for k = 3
0 - 000 - aaa
1 - 001 - aab
2 - 010 - aba
etc

Quote:

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Originally Posted by vart

External loop is on string length
Internal - is just a binary counter from 0 to 2^k-1
for example for k = 3
0 - 000 - aaa
1 - 001 - aab
2 - 010 - aba
etc

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But again, that's not the sequence he wants. What he wants is a lexicographic ordering of all strings of a's and b's. That is NOT the same as simple digital counting.

EDIT: I'm stupid. Didn't fully comprehend what you wrote. Your method is right :)

Wow MacGyver you must really want a death ray :|

Quote:

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Originally Posted by Salem

> It 's NOT exactly like binary counting
Close enough though.
Once you understand base 2 counting, plus I take it you already understand base 10 counting, then figuring out base 26 counting should be easy.

---

Binary counting is not enaugh becauce has a 2^k limit (k=32 or 64) .I need combinations up to 1000 caracters(2^1000!!!).
If this is easier i want this order 1-digit , 2-digit ..... n-digit (combinations )
No problem if "bb" is before "ab" but a 5-digit combination cant be after a 6-digit combination.

Quote:

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I need combinations up to 1000 caracters

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So? What is the problem?

Quote:

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Originally Posted by vart

So? What is the problem?

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I cant write : for(int i=0; i<2^500;i++)
I think is better working with strings.

Code:

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char* incrementString(char* str)
{
  size_t len = strlen(str);
  size_t index;
  for(index = len; index > 0; index--)
  {
      if(str[index-1] == 'a')
      {
        str[index-1] = 'b'; /* and exit */
        return str;
      }
      /* we have 'b' - increment it and go to the next char */
      str[index-1] = 'a';
  }
  /* all chars were 'b' - now they all are reset to 'a'
    * return NULL pointer to indicate the end of iterations
    * calling function should append 'a' to the string and run the loop again
    * if the desired string length  is not achieved
    */
  return NULL;
}

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Have not compiled or tested the code - but hope it shows the idea of incrementing arbitrary length string