From 1f93e69adfbe8830c0ef47a24e07a7f333168dd4 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Thu, 4 Jan 2024 23:30:17 +0100
Subject: solution for day 4

---
 2020/src/day04.cpp | 132 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 132 insertions(+)
 create mode 100644 2020/src/day04.cpp

diff --git a/2020/src/day04.cpp b/2020/src/day04.cpp
new file mode 100644
index 0000000..63f8c92
--- /dev/null
+++ b/2020/src/day04.cpp
@@ -0,0 +1,132 @@
+#include <algorithm>
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <iterator>
+#include <map>
+#include <sstream>
+#include <string>
+#include <vector>
+using namespace std;
+
+auto
+split(string_view line, string_view delimiter)
+{
+	size_t pos_start = 0;
+	size_t pos_end   = 0;
+
+	vector<string> res;
+
+	while ( (pos_end = line.find(delimiter, pos_start)) != string::npos ) {
+		auto token = line.substr(pos_start, pos_end - pos_start);
+		pos_start  = pos_end + delimiter.length();
+
+		res.emplace_back(token);
+	}
+
+	if ( pos_start != line.size() ) {
+		res.emplace_back(line.substr(pos_start));
+	}
+	return res;
+}
+
+auto
+read_file(string_view filename)
+{
+	fstream    input{ filename };
+	const auto passports = split(string{ istreambuf_iterator<char>{ input }, istreambuf_iterator<char>{} }, "\n\n");
+
+	vector<map<string, string>> result;
+
+	for ( const auto& passport: passports ) {
+		map<string, string> bar;
+		stringstream        foo{ passport };
+		for ( string keyval; foo >> keyval; ) {
+			auto colon = keyval.find(':');
+			auto key   = keyval.substr(0, colon);
+			auto val   = keyval.substr(colon + 1);
+			bar[key]   = val;
+		}
+		result.emplace_back(bar);
+	}
+
+	return result;
+}
+
+auto
+contains_all_fields(const map<string, string>& passport)
+{
+	static const array<string, 7> keys = { "byr", "iyr", "eyr", "hgt", "hcl", "ecl", "pid" };
+	return all_of(keys.begin(), keys.end(), [&](auto key) { return passport.contains(key); });
+}
+
+void
+part1(const vector<map<string, string>>& passports)
+{
+	cout << count_if(passports.begin(), passports.end(), contains_all_fields) << endl;
+}
+
+void
+part2(const vector<map<string, string>>& passports)
+{
+	auto check_birth_year = [](const map<string, string>& passport) {
+		auto year = stoi(passport.at("byr"));
+		return 1920 <= year && year <= 2002;
+	};
+
+	auto check_issue_year = [](const map<string, string>& passport) {
+		auto year = stoi(passport.at("iyr"));
+		return 2010 <= year && year <= 2020;
+	};
+
+	auto check_expiration_year = [](const map<string, string>& passport) {
+		auto year = stoi(passport.at("eyr"));
+		return 2020 <= year && year <= 2030;
+	};
+
+	auto check_height = [](const map<string, string>& passport) {
+		auto height_str = passport.at("hgt");
+		auto height     = stoi(height_str);
+		return (height_str.ends_with("in") && 59 <= height && height <= 76) ||
+		       (height_str.ends_with("cm") && 150 <= height && height <= 193);
+	};
+
+	auto check_hair_color = [](const map<string, string>& passport) {
+		auto hair = passport.at("hcl");
+		return hair.length() == 7 && hair.starts_with('#') && hair.find_first_not_of("0123456789abcdef", 1) == string::npos;
+	};
+
+	auto check_eye_color = [](const map<string, string>& passport) {
+		const array<string, 7> valid = { "amb", "blu", "brn", "gry", "grn", "hzl", "oth" };
+		return find(valid.begin(), valid.end(), passport.at("ecl")) != valid.end();
+	};
+
+	auto check_passport_id = [](const map<string, string>& passport) {
+		auto pid = passport.at("pid");
+		return pid.length() == 9 && pid.find_first_not_of("0123456789") == string::npos;
+	};
+
+	const array<function<bool(const map<string, string>&)>, 8> checks = {
+		contains_all_fields,
+		check_birth_year,
+		check_issue_year,
+		check_expiration_year,
+		check_height,
+		check_hair_color,
+		check_eye_color,
+		check_passport_id
+	};
+
+	cout << count_if(passports.begin(), passports.end(), [&checks](const map<string, string>& passport) {
+		return all_of(checks.begin(), checks.end(), [&passport](auto check) { return check(passport); });
+	}) << endl;
+}
+
+int
+main()
+{
+	auto passports = read_file("data/day04.txt");
+
+	part1(passports);
+	part2(passports);
+}
-- 
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