Power set generated by bits

Question

I have this code which generates power set of an array of size 4 (number is just example, less combinations to write...).

#define ARRAY_SIZE 4


unsigned int i,          


        

Answer 1

• I started with a simple recursive permutation generator.
• Added a length parameter and, when the length reaches 0, instead of permuting further, just print the string we have so far.
• Added a position where we must continue picking characters from.

The code:

(I know some people don't like raw arrays / pointers, but it's so much easier to get great performance for this problem with that as opposed to pretty containers)

void powerSet(char *arr, int arrLen, int pos, int startPos, int length)
{
   if (length == 0)
      printf("%.*s\n", pos, arr);
   else
      for (int i = startPos; i < arrLen; i++)
      {
         std::swap(arr[pos], arr[i]);
         powerSet(arr, arrLen, pos+1, i+1, length - 1);
         std::swap(arr[pos], arr[i]);
      }
}

And the calling function:

void powerSet(char *arr, int arrLen)
{
    for (int i = 1; i <= arrLen; i++)
      powerSet(arr, 4, 0, 0, i);
}

powerSet("1234", 4) prints:

1
2
3
4
12
13
14
23
24
34
123
124
134
234
1234

Test.