Add Problem 2 solution

c++/main.cpp

@@ -6,14 +6,20 @@
 
 using namespace std; 
 
-int main() {
-    auto x = solve1;
+int main(int argc, char *argv[]) {
+    if (argc < 2) {
+        return 0;
+    }
+    int problem_number = stoi(string(argv[1]));
+    solution_fn solutions[] = {solve1, solve2};
+    auto x = solutions[problem_number-1];
     auto answer = x(cin);
     cout << "Solution 1: " << answer.first << endl;
     cout << "Solution 2: " << answer.second << endl;
     return 0;
 }
 
+
 //istream get_input() {
 //    CURL *curl;
 //    CURLcode res;
@@ -28,3 +34,8 @@ int main() {
 //
 //    curl_global_cleanup();
 //}
+// TODO: automatically download input files and stuff
+//    char *home_dir = getenv("HOME");
+//    if (home_dir != NULL) {
+//
+//    }

c++/problem2.cpp

@@ -0,0 +1,39 @@
+#include <sstream>
+#include <cstdint>
+#include <stdexcept>
+#include "solutions.hpp"
+
+using namespace std;
+
+pair<string, string> solve2(istream& input) {
+    uint64_t part1 = 0, part2 = 0;
+    for (string line; getline(input, line); ) {
+        stringstream line_stream(line);
+        int64_t min_count, max_count;
+        char target;
+        string password;
+        line_stream >> min_count;
+        if (line_stream.get() != (int) '-') {
+            throw domain_error("input incorrect");
+        }
+        line_stream >> max_count;
+        if (line_stream.get() != (int) ' ') {
+            throw domain_error("input incorrect");
+        }
+        line_stream >> target;
+        if (line_stream.get() != (int) ':') {
+            throw domain_error("input incorrect");
+        }
+        if (line_stream.get() != (int) ' ') {
+            throw domain_error("input incorrect");
+        }
+        line_stream >> password;
+        size_t count = 0;
+        for (char c : password) {
+            count+=(int)(c == target);
+        }
+        part1 += (int)(count >= min_count && count <= max_count);
+        part2 += (int)((password[min_count - 1] == target) != (password[max_count - 1] == target));
+    }
+    return pair(to_string(part1), to_string(part2));
+}

c++/solutions.hpp

@@ -4,6 +4,8 @@
 #include <utility>
 #include <string>
 
+typedef std::pair<std::string, std::string> (*solution_fn)(std::istream&);
 #define DECL_SOLUTION(x) std::pair<std::string, std::string> solve##x(std::istream&);
 
 DECL_SOLUTION(1)
+DECL_SOLUTION(2)