#include <cstdio>
#include <algorithm>
 
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]);
      }
}
 
void powerSet(char *arr, int arrLen)
{
    for (int i = 1; i <= arrLen; i++)
      powerSet(arr, 4, 0, 0, i);
}
 
int main()
{
    char arr[] = "1234";
    powerSet(arr, 4);
    return 0;
}

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