Add problem 4

.gitignore

@@ -0,0 +1 @@
+/c++/aoc-cpp

c++/main.cpp

@@ -11,7 +11,7 @@ int main(int argc, char *argv[]) {
         return 0;
     }
     int problem_number = stoi(string(argv[1]));
-    solution_fn solutions[] = {solve1, solve2, solve3};
+    solution_fn solutions[] = {solve1, solve2, solve3, solve4};
     auto x = solutions[problem_number-1];
     auto answer = x(cin);
     cout << "Solution 1: " << answer.first << endl;

c++/problem4.cpp

@@ -0,0 +1,88 @@
+#include <iterator>
+#include <sstream>
+#include <unordered_set>
+#include <unordered_map>
+#include <functional>
+#include <algorithm>
+#include <cctype>
+
+#include "solutions.hpp"
+
+using namespace std;
+
+bool is_digit(char c) {
+    return isdigit((int) c);
+}
+
+bool is_hex_digit(char c) {
+    return isdigit((int) c) || (c >= 'a' && c <= 'f');
+}
+
+pair<string, string> solve4(istream& input) {
+    cerr << boolalpha;
+    stringstream current_passport{string()};
+    uint64_t part1 = 0, part2 = 0;
+    unordered_map<string, function<bool(string&)>> valid_funcs;
+    valid_funcs["byr"] = [](string &value) {
+        int int_value = stoi(value);
+        return value.length() == 4 && all_of(value.begin(), value.end(), is_digit) && int_value >= 1920 && int_value <= 2002;
+    };
+    valid_funcs["iyr"] = [](string &value) {
+        int int_value = stoi(value);
+        return value.length() == 4 && all_of(value.begin(), value.end(), is_digit) && int_value >= 2010 && int_value <= 2020;
+    };
+    valid_funcs["eyr"] = [](string &value) {
+        int int_value = stoi(value);
+        return value.length() == 4 && all_of(value.begin(), value.end(), is_digit) && int_value >= 2020 && int_value <= 2030;
+    };
+    valid_funcs["hgt"] = [](string &value) {
+        int int_value = stoi(value);
+        return (value.length() == to_string(int_value).length() + 2) && (
+                (value.ends_with("in") && int_value >= 59 && int_value <= 76) ||
+                (value.ends_with("cm") && int_value >= 150 && int_value <= 193)
+                );
+    };
+    valid_funcs["hcl"] = [](string &value) {
+        auto it = value.begin();
+        return value.length() == 7 && *it == '#' && all_of(next(it), value.end(), is_hex_digit);
+    };
+    valid_funcs["ecl"] = [](string &value) {
+        unordered_set<string> valid_eye_colors = { {
+            "amb"s, "blu"s, "brn"s, "gry"s, "grn"s, "hzl"s, "oth"s
+        } };
+        return valid_eye_colors.contains(value);
+    };
+    valid_funcs["pid"] = [](string &value) {
+        return value.length() == 9 && all_of(value.begin(), value.end(), is_digit);
+    };
+
+    for (string line; getline(input, line); ) {
+        if (!line.empty()) { // append to existing passport
+            if (!current_passport.eof()) {
+                current_passport << ' ';
+            }
+            current_passport << line;
+        }
+        if (line.empty() || input.peek() == EOF) { // no input; parse current passport
+            unordered_set<string> mandatory_fields = {
+                { "byr"s, "iyr"s, "eyr"s, "hgt"s, "hcl"s, "ecl"s, "pid"s}
+            };
+            bool all_fields_valid = true;
+            for (string entry; getline(current_passport, entry, ' '); ) {
+                auto field_delim_pos = entry.find(':');
+                if (field_delim_pos != string::npos) {
+                    string field_name = entry.substr(0, field_delim_pos);
+                    string field_value = entry.substr(field_delim_pos+1);
+                    mandatory_fields.erase(field_name);
+                    if (valid_funcs.contains(field_name)) {
+                        all_fields_valid = all_fields_valid && valid_funcs[field_name](field_value);
+                    }
+                }
+            }
+            current_passport.clear();
+            part1 += (uint64_t) mandatory_fields.empty();
+            part2 += (uint64_t) (mandatory_fields.empty() && all_fields_valid);
+        }
+    }
+    return pair(to_string(part1), to_string(part2));
+}

c++/solutions.hpp

@@ -10,3 +10,4 @@ typedef std::pair<std::string, std::string> (*solution_fn)(std::istream&);
 DECL_SOLUTION(1)
 DECL_SOLUTION(2)
 DECL_SOLUTION(3)
+DECL_SOLUTION(4)