My code

… was written in C++11 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>
       
#include <vector>
       
 
       
#define ORIGINAL
       
 
       
// number of ways to choose n elements from k available

       
unsigned long long choose(unsigned long long n, unsigned long long k)
       
{
       
  // n! / (n-k)!k!
       
  unsigned long long result = 1;
       
  // reduce overflow by dividing as soon as possible to keep numbers small
       
  for (unsigned long long invK = 1; invK <= k; invK++)
       
  {
       
    result *= n;
       
    result /= invK;
       
    n--;
       
  }
       
  return result;
       
}
       
 
       
int main()
       
{
       
  unsigned int tests;
       
  std::cin >> tests;
       
  while (tests--)
       
  {
       
    // length of row
       
    unsigned int totalLength = 50;
       
    std::cin >> totalLength;
       
 
       
    unsigned long long sum = 0;
       
    // try all four block lengths
       
    for (unsigned int blockLength = 2; blockLength <= 4; blockLength++)
       
    {
       
      // maximum number of blocks of the current size
       
      auto maxBlocks = totalLength / blockLength;
       
 
       
      // insert 1 to maxBlocks colored blocks
       
      for (unsigned int colored = 1; colored <= maxBlocks; colored++)
       
      {
       
        // remaining black tiles
       
        auto black = totalLength - colored * blockLength;
       
        // total number of black and colored tiles
       
        auto tiles = black + colored;
       
        // count combinations
       
        auto combinations = choose(tiles, colored);
       
        sum += combinations;
       
 
       
#ifndef ORIGINAL
       
        // Hackerrank only
       
        sum %= 1000000007;
       
#endif
       
      }
       
    }
       
 
       
    std::cout << sum << std::endl;
       
  }
       
 
       
  return 0;
       
}

This solution contains 8 empty lines, 11 comments and 5 preprocessor commands.