1 files changed, 132 insertions, 0 deletions

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);
+}