Solve Day 3 C++

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};
+    solution_fn solutions[] = {solve1, solve2, solve3};
     auto x = solutions[problem_number-1];
     auto answer = x(cin);
     cout << "Solution 1: " << answer.first << endl;

c++/problem3.cpp

@@ -0,0 +1,42 @@
+#include <vector>
+#include <utility>
+#include <array>
+
+#include "solutions.hpp"
+
+using namespace std;
+
+pair<string, string> solve3(istream& input) {
+    vector<string> my_map;
+    uint64_t width;
+    bool width_set = false;
+    for (string line; getline(input, line); ) {
+        my_map.push_back(line);
+        if (!width_set) {
+            width = line.length();
+            width_set = true;
+        }
+    }
+    array<pair<uint64_t, uint64_t>, 5> slopes { {
+        {1, 1},
+        {3, 1},
+        {5, 1},
+        {7, 1},
+        {1, 2}
+    } };
+    uint64_t product = 1;
+    uint64_t part1;
+    for (auto slope : slopes) {
+        uint64_t total_trees = 0;
+        for (auto pos = pair(0, 0); pos.second < my_map.size(); ) {
+            total_trees += (int) my_map[pos.second][pos.first] == '#';
+            pos.first = (pos.first + slope.first) % width;
+            pos.second += slope.second;
+        }
+        product *= total_trees;
+        if (slope.first == 3 && slope.second == 1) {
+            part1 = total_trees;
+        }
+    }
+    return pair(to_string(part1), to_string(product));
+}

c++/solutions.hpp

@@ -9,3 +9,4 @@ typedef std::pair<std::string, std::string> (*solution_fn)(std::istream&);
 
 DECL_SOLUTION(1)
 DECL_SOLUTION(2)
+DECL_SOLUTION(3)