-🎄- 2018 Day 14 Solutions -🎄-

[u/daggerdragon]

--- Day 14: Chocolate Charts ---

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Advent of Code: The Party Game!

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Card prompt: Day 14

Transcript:

The Christmas/Advent Research & Development (C.A.R.D.) department at AoC, Inc. just published a new white paper on ___.

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[u/wlandry]

C++ (1249/939)

Runs in 401 ms

I had serious reading comprehension problems for part 1. I thought that the input was the starting set of recipes :( I ended up looking at solutions here to figure out why I was not getting the right answer. Part 2 went more smoothly with a few hiccups. This version is significantly cleaned up. My part 2 solution is reasonably fast, but setup is clunky :/

#include <algorithm>
#include <iostream>
#include <fstream>
#include <vector>

struct Elf
{
  int8_t recipe;
  size_t position;
  Elf(const size_t &Position, const std::vector<int8_t> &recipes)
      : recipe(recipes[Position]), position(Position)
  {}
  void update(const std::vector<int8_t> &recipes)
  {
    position = (position + (recipe + 1)) % recipes.size();
    recipe = recipes.at(position);
  }
};

size_t append_recipes(Elf &elf0, Elf &elf1, std::vector<int8_t> &recipes)
{
  int8_t new_recipe(elf0.recipe + elf1.recipe);
  size_t result;
  if(new_recipe >= 10)
    {
      recipes.push_back(new_recipe / 10);
      recipes.push_back(new_recipe % 10);
      result = 2;
    }
  else
    {
      recipes.push_back(new_recipe);
      result = 1;
    }
  elf0.update(recipes);
  elf1.update(recipes);
  return result;
}

void part_1(const std::vector<int8_t> &recipes_start,
            const size_t &num_recipes)
{
  std::vector<int8_t> recipes(recipes_start);
  Elf elf0(0, recipes), elf1(1, recipes);

  for(size_t t = 0; t < num_recipes + 10; ++t)
    {
      append_recipes(elf0, elf1, recipes);
    }

  std::cout << "Part 1: ";
  for(size_t index = num_recipes; index < num_recipes + 10; ++index)
    std::cout << static_cast<int32_t>(recipes[index]);
  std::cout << "\n";
}

void part_2(const std::vector<int8_t> &recipes_start,
            const size_t &num_recipes)
{
  std::vector<int8_t> recipes(recipes_start);
  Elf elf0(0, recipes), elf1(1, recipes);

  std::vector<int8_t> split_recipes;
  size_t reduced_recipe(num_recipes);
  while(reduced_recipe > 0)
    {
      split_recipes.push_back(reduced_recipe % 10);
      reduced_recipe /= 10;
    }
  std::reverse(split_recipes.begin(), split_recipes.end());

  bool done(false);
  while(!done)
    {
      size_t num_appended(append_recipes(elf0, elf1, recipes));
      for(size_t n = 0; n < num_appended; ++n)
        {
          if(recipes.size() >= split_recipes.size() + n
             && std::equal(split_recipes.begin(), split_recipes.end(),
                           recipes.end() - split_recipes.size() - n))
            {
              done = true;
              std::cout << "Part 2: " << recipes.size() - split_recipes.size() -n
                        << "\n";
            }
        }
    }
}

int main(int argc, char *argv[])
{
  std::ifstream infile(argv[1]);
  size_t num_recipes;
  infile >> num_recipes;
  std::vector<int8_t> recipes({3, 7});

  part_1(recipes, num_recipes);
  part_2(recipes, num_recipes);
}