Solve problem 5

c++/main.cpp

@@ -1,21 +1,55 @@
 #include <iostream>
 #include <utility>
+#include <sstream>
 #include <string>
-
+#include <array>
+#include <stdexcept>
+#include <functional>
 #include "solutions.hpp"
 
 using namespace std; 
 
+typedef std::pair<std::string, std::string>(*solution_t)(std::istream&);
+template <unsigned long N> void init_solutions(std::array<solution_t, N> &solutions);
+
+template <unsigned int N>
+pair<string, string> solve(istream&) {
+    stringstream s;
+    s << "solution " << N << " not implemented";
+    throw logic_error(s.str());
+}
+
+template <unsigned long I>
+constexpr void do_init(solution_t *solutions) {
+    solutions[I-1] = solve<I>;
+    do_init<I-1>(solutions);
+}
+
+template <>
+constexpr void do_init<1>(solution_t *solutions) {
+    solutions[0] = solve<1>;
+}
+
+template <unsigned long N>
+void init_solutions(array<solution_t, N> &solutions) {
+    do_init<N>(solutions.data());
+}
+
 int main(int argc, char *argv[]) {
+    array<pair<string,string>(*)(istream&), 25> solutions;
+    init_solutions(solutions);
     if (argc < 2) {
         return 0;
     }
     int problem_number = stoi(string(argv[1]));
-    solution_fn solutions[] = {solve1, solve2, solve3, solve4};
-    auto x = solutions[problem_number-1];
+    try {
+    auto x = solutions.at(problem_number-1);
     auto answer = x(cin);
     cout << "Solution 1: " << answer.first << endl;
     cout << "Solution 2: " << answer.second << endl;
+    } catch (exception const &e) {
+        cerr << "error: " << e.what() << endl;
+    }
     return 0;
 }
 

c++/problem1.cpp

@@ -12,7 +12,8 @@
 
 using namespace std;
 
-pair<string, string> solve1(istream &input) {
+template <>
+pair<string, string> solve<1>(istream &input) {
     unordered_set<int64_t> seen;
     unordered_map<int64_t, pair<int64_t, int64_t>> targets;
     string part1;

c++/problem2.cpp

@@ -5,7 +5,8 @@
 
 using namespace std;
 
-pair<string, string> solve2(istream& input) {
+template <>
+pair<string, string> solve<2>(istream& input) {
     uint64_t part1 = 0, part2 = 0;
     for (string line; getline(input, line); ) {
         stringstream line_stream(line);

c++/problem3.cpp

@@ -6,7 +6,8 @@
 
 using namespace std;
 
-pair<string, string> solve3(istream& input) {
+template<>
+pair<string, string> solve<3>(istream& input) {
     vector<string> my_map;
     uint64_t width;
     bool width_set = false;

c++/problem4.cpp

@@ -18,7 +18,8 @@ bool is_hex_digit(char c) {
     return isdigit((int) c) || (c >= 'a' && c <= 'f');
 }
 
-pair<string, string> solve4(istream& input) {
+template <>
+pair<string, string> solve<4>(istream& input) {
     cerr << boolalpha;
     stringstream current_passport{string()};
     uint64_t part1 = 0, part2 = 0;

c++/problem5.cpp

@@ -0,0 +1,32 @@
+#include <bitset>
+#include "solutions.hpp"
+
+using namespace std;
+
+template <>
+pair<string, string> solve<5>(istream& input) {
+    uint64_t max_seatid = 0;
+    size_t part2 = 0;
+    bitset<1024> taken_seats;
+    for (string line; getline(input, line); ) {
+        uint64_t seatid = 0;
+        for (auto c : line) {
+            seatid <<= 1;
+            switch (c) {
+                case 'B':
+                case 'R':
+                    seatid++;
+            }
+        }
+        max_seatid = max(seatid, max_seatid);
+        taken_seats.set(seatid);
+    }
+    for (size_t i = 1; i < taken_seats.size(); ++i) {
+        if (taken_seats[i-1] && taken_seats[i+1] && !taken_seats[i]) {
+            part2 = i;
+            break;
+        }
+    }
+
+    return pair(to_string(max_seatid), to_string(part2));
+}

c++/solutions.hpp

@@ -3,11 +3,6 @@
 #include <iostream>
 #include <utility>
 #include <string>
+#include <array>
 
-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)
-DECL_SOLUTION(3)
-DECL_SOLUTION(4)
+template <unsigned int N> std::pair<std::string, std::string> solve(std::istream&);