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.

       
#include <iostream>
       
#include <string>
       
#include <algorithm>
       
 
       
int main()
       
{
       
  // can't start with an 'A' or 'B'
       
  std::string train = "CABDEFGHIJKLM"; // up to 14 for live test
       
 
       
  // look for the 2011th maximix train
       
  auto stopWhenFound = 2011;
       
  auto numFound = 0;
       
 
       
  // shorter train
       
  auto length = train.size();
       
  std::cin >> length >> stopWhenFound;
       
  train.erase(length);
       
 
       
  // two for each carriage, except for the last two which require just one rotation
       
  unsigned int maxRotations = (train.size() - 1) * 2 - 1;
       
 
       
  do
       
  {
       
    auto current = train;
       
    // move carriage 'A', then 'B', then 'C', ... to its correct position
       
    auto expect  = 'A';
       
 
       
    // count rotations
       
    unsigned int rotations = 0;
       
    for (size_t i = 0; i < current.size() - 1; i++, expect++)
       
    {
       
      // carriage already in correct position ?
       
      // => can't be a maximix arrangement
       
      if (current[i] == expect)
       
        break;
       
      // carriage in last position ? only allowed for 'J' (the second-to-last carriage)
       
      if (current[current.size() - 1] == expect && i != current.size() - 2)
       
        break;
       
 
       
      // find carriage
       
      auto j = i + 1;
       
      while (current[j] != expect)
       
        j++;
       
 
       
      // rotate carriage to the end of the train (unless it's already there)
       
      if (j < current.size() - 1)
       
      {
       
        std::reverse(current.begin() + j, current.end());
       
        rotations++;
       
      }
       
 
       
      // rotate carriage to its correct position
       
      std::reverse(current.begin() + i, current.end());
       
      rotations++;
       
    }
       
 
       
    // is it a maximix arrangement ?
       
    if (rotations == maxRotations)
       
    {
       
      numFound++;
       
      // found 2011th maximix ?
       
      if (numFound == stopWhenFound)
       
        break;
       
    }
       
  } while (std::next_permutation(train.begin(), train.end()));
       
 
       
  std::cout << train << std::endl;
       
  return 0;
       
}

This solution contains 11 empty lines, 14 comments and 3 preprocessor commands.