1 files changed, 78 insertions, 0 deletions

diff --git a/2023/08/src/part2.cpp b/2023/08/src/part2.cpp
new file mode 100644
index 0000000..23b456d
--- /dev/null
+++ b/2023/08/src/part2.cpp
@@ -0,0 +1,78 @@
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <unordered_map>
+#include <vector>
+#include <numeric>
+
+#include "util.h"
+
+using Pos = std::string;
+using Moves = std::vector<bool>;
+using Map = std::unordered_map<Pos,std::pair<Pos,Pos>>;
+
+constexpr char EQUAL[] = "=";
+
+std::pair<Moves,Map> parse(const char* path)
+{
+    Map map{};
+    Moves moves{};
+
+    std::ifstream input{ path };
+    if (input.is_open())
+    {
+        std::string line;
+        std::getline(input,line);
+
+        moves.resize(line.size());
+        std::transform(line.cbegin(), line.cend(),
+            moves.begin(), [](unsigned char c) { return c == 'L'; });
+
+        std::string from, tol, tor;
+        while (not std::getline(input,line).eof())
+        {
+            if (line.empty()) continue;
+
+            std::istringstream in{ line };
+            in >> from >> util::skip<EQUAL> >> tol >> tor;
+            tol.erase(0,1); tol.pop_back();
+            tor.pop_back();
+            map.insert({ from, { tol, tor } });
+        }
+    }
+    input.close();
+
+    return { std::move(moves), std::move(map) };
+}
+
+long long compute(const Map& map, const Moves& moves, Pos pos)
+{
+    long long idx{};
+
+    while (pos[2] != 'Z')
+    {
+        bool left = moves[idx++ % moves.size()];
+        pos = left ? map.at(pos).first : map.at(pos).second; 
+    }
+
+    return idx;
+}
+
+int main(int argc, char* argv[])
+{
+    long long answer{ 1 };
+
+    auto [moves, map] = parse(argv[1]);
+
+    for (const auto& kv : map)
+    {
+        if (kv.first[2] == 'A')
+        {
+            answer = std::lcm(answer, compute(map, moves, kv.first));
+        }
+    }
+
+    std::cout << answer << std::endl;
+    return 0;
+}
+