aocpp/2019/04.cpp

#include <algorithm>
#include <cstdint>
#include <iostream>
#include <tuple>
#include <fstream>
#include <iterator>
#include <vector>

#include <aocpp/Startup.hpp>

namespace {

auto Parse(std::istream & in) -> std::pair<std::int64_t, std::int64_t> {
  std::int64_t lo, hi;
  std::string line;
  std::getline(in, line, '-');
  lo = std::stol(std::move(line));
  std::getline(in, line);
  hi = std::stol(std::move(line));
  return {lo,hi};
}

auto Valid1(std::string const& str) {
  for (std::size_t i = 1; i < str.size(); i++) {
    if (str[i-1] == str[i]) {
      return true;
    }
  }
  return false;
}

auto Valid2(std::string const& str) {
   for (std::size_t i = 1; i < str.size(); i++) {
    if (                        str[i] == str[i-1] &&
        (i == str.size() - 1 || str[i] != str[i+1]) &&
        (i == 1              || str[i] != str[i-2]))
    {
      return true;
    }
  }
  return false;
}

} // namespace

auto Main(std::istream & in, std::ostream & out) -> void
{
  auto const [lo,hi] = Parse(in);

  std::int64_t part1 = 0;
  std::int64_t part2 = 0;

  for (auto i = lo; i <= hi; i++) {
    auto str = std::to_string(i);
    if (std::is_sorted(str.begin(), str.end())) {
      if (Valid1(str)) part1++;
      if (Valid2(str)) part2++;
    }
  }

  out << "Part 1: " << part1 << std::endl;
  out << "Part 2: " << part2 << std::endl;
}