My code

… was written in C++ and can be compiled with G++, Clang++, Visual C++. You can download it, too. Or just jump to my GitHub repository.

The code contains #ifdefs to switch between the original problem and the Hackerrank version.
Enable #ifdef ORIGINAL to produce the result for the original problem (default setting for most problems).

       
#include <iostream>
       
 
       
int main()
       
{
       
  unsigned int maxFactor, maxDigit;  // 10000 and 9 for the original problem
       
  std::cin >> maxFactor >> maxDigit;
       
 
       
  // bitmask if all digits are used
       
  unsigned int bitsAll = 0;
       
  for (unsigned int i = 1; i <= maxDigit; i++)
       
    bitsAll |= 1 << i;
       
 
       
#define ORIGINAL
       
#ifdef ORIGINAL
       
  // largest pandigital number found so far
       
  unsigned int largest = 0;
       
#endif
       
 
       
  // try all numbers
       
  for (unsigned int i = 2; i <= maxFactor; i++)
       
  {
       
    // the whole pandigital number
       
    unsigned int pandigital = 0;
       
 
       
    // multiply i by 1,2,3,...
       
    unsigned int multiplier = 1;
       
 
       
    // bitmask of used digits (nth bit is set if pandigital contains digit n)
       
    unsigned int bitsUsed   = 0;
       
 
       
    while (bitsUsed < bitsAll)
       
    {
       
      // next step
       
      unsigned int product = i * multiplier;
       
 
       
      // extract right-most digit
       
      while (product > 0)
       
      {
       
        // extract right-most digit
       
        unsigned int digit = product % 10;
       
        // remove it
       
        product    /= 10;
       
 
       
        // make room to add i*multiplier lateron
       
        pandigital *= 10;
       
 
       
        // remember all digits we used
       
        unsigned int bitMask = 1 << digit;
       
        // we already had this digit ?
       
        if (digit == 0 || (bitsUsed & bitMask) != 0)
       
        {
       
          bitsUsed = bitsAll + 1; // set to an invalid value
       
          break;
       
        }
       
 
       
        // mark current digit as "used"
       
        bitsUsed |= bitMask;
       
      }
       
 
       
      // keep going in the sequence
       
      pandigital += i * multiplier;
       
      multiplier++;
       
    }
       
 
       
    // enough digits generated ?
       
    if (bitsUsed == bitsAll)
       
    {
       
#ifdef ORIGINAL
       
      if (largest < pandigital)
       
        largest = pandigital;
       
#else
       
      std::cout << i << std::endl;
       
#endif
       
    }
       
  }
       
 
       
#ifdef ORIGINAL
       
  std::cout << largest << std::endl;
       
#endif
       
 
       
  return 0;
       
}

This solution contains 15 empty lines, 16 comments and 9 preprocessor commands.