day_04b.cpp

#include <algorithm>
#include <fstream>
#include <iostream>
#include <string>
#include <unordered_map>
#include <unordered_set>

int main() {
  std::ifstream file;
  file.open("../input/day_04_input");
  std::string text;
  int count = 0;
  int fields = 0;
  std::unordered_set<std::string> key_fields{"byr", "iyr", "eyr", "hgt",
                                             "hcl", "ecl", "pid"};
  std::unordered_map<std::string, bool (*)(const std::string&)> rules{
      {"byr",
       [](const std::string& val) {
         const int i_val = std::stoi(val);
         return i_val >= 1920 && i_val <= 2002;
       }},
      {"iyr",
       [](const std::string& val) {
         const int i_val = std::stoi(val);
         return i_val >= 2010 && i_val <= 2020;
       }},
      {"eyr",
       [](const std::string& val) {
         const int i_val = std::stoi(val);
         return i_val >= 2020 && i_val <= 2030;
       }},
      {"hgt",
       [](const std::string& val) {
         const std::string unit = val.substr(val.size() - 2, 2);
         if (unit == "cm") {
           const int i_val = stoi(val.substr(0, val.size() - 2));
           return i_val >= 150 && i_val <= 193;
         } else if (unit == "in") {
           const int i_val = stoi(val.substr(0, val.size() - 2));
           return i_val >= 59 && i_val <= 76;
         } else
           return false;
       }},
      {"hcl",
       [](const std::string& val) {
         return val.size() == 7 && val[0] == '#' &&
                (val.substr(1, val.size())
                     .find_first_not_of("0123456789abcdef") ==
                 std::string::npos);
       }},
      {"ecl",
       [](const std::string& val) {
         const std::unordered_set<std::string> allowed_vals{
             "amb", "blu", "brn", "gry", "grn", "hzl", "oth"};
         return allowed_vals.find(val) != allowed_vals.end();
       }},
      {"pid", [](const std::string& val) {
         return val.size() == 9 &&
                (val.find_first_not_of("0123456789") == std::string::npos);
       }}};

  while (std::getline(file, text)) {
    text.erase(std::remove_if(std::begin(text), std::end(text),
                              [](char c) { return !std::isprint(c); }),
               std::end(text));
    if (text.empty()) {
      if (fields == 7) {
        ++count;
      }
      fields = 0;
      continue;
    }

    const std::string delimiter = " ";
    size_t start = 0;
    size_t end = text.find_first_of(delimiter);
    while (end != std::string::npos) {
      const size_t pos_colon = text.find(':', start);
      const std::string key = text.substr(start, pos_colon - start);
      const std::string val = text.substr(pos_colon + 1, end - pos_colon - 1);
      if (key_fields.find(key) != key_fields.end() && rules[key](val)) {
        ++fields;
      }
      start = end + 1;
      end = text.find_first_of(delimiter, start);
    }
    const size_t pos_colon = text.find(':', start);
    const std::string key = text.substr(start, pos_colon - start);
    const std::string val =
        text.substr(pos_colon + 1, text.size() - pos_colon - 1);
    if (key_fields.find(key) != key_fields.end() && rules[key](val)) {
      ++fields;
    }
    start = end + 1;
    end = text.find_first_of(delimiter, start);
  }

  if (fields == 7) {
    ++count;
  }
  std::cout << count << '\n';
  return count;
}