1 files changed, 85 insertions, 0 deletions

diff --git a/2025/src/day11.cpp b/2025/src/day11.cpp
new file mode 100644
index 0000000..47440f9
--- /dev/null
+++ b/2025/src/day11.cpp
@@ -0,0 +1,85 @@
+#include <filesystem>
+#include <fstream>
+#include <functional>
+#include <iostream>
+#include <map>
+#include <set>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+using Graph = map<string, set<string>>;
+
+vector<string>
+split(const string& str, const string& delims)
+{
+        vector<string> result;
+
+        size_t start = str.find_first_not_of(delims);
+        while ( start != string::npos ) {
+                size_t end = str.find_first_of(delims, start);
+
+                if ( end == string::npos ) {
+                        // letzter Teil
+                        result.push_back(str.substr(start));
+                        break;
+                }
+
+                result.push_back(str.substr(start, end - start));
+
+                start = str.find_first_not_of(delims, end);
+        }
+
+        return result;
+}
+
+Graph
+read_file(const filesystem::path& filename)
+{
+        ifstream file{ filename };
+
+        Graph graph;
+        for ( string line; getline(file, line); ) {
+                auto parts = split(line, ": ");
+                graph[parts[0]].insert(parts.begin() + 1, parts.end());
+        }
+        return graph;
+}
+
+void
+part1(const Graph& graph)
+{
+        map<string, long> cache;
+
+        function<long(const string&)> dfs = [&](const string& src) {
+                if ( src == "out" ) {
+                        return 1L;
+                }
+
+                if ( cache.contains(src) ) {
+                        return cache.at(src);
+                }
+
+                long count = 0;
+
+                for ( const auto& node: graph.at(src) ) {
+                        count += dfs(node);
+                }
+
+                return cache[src] = count;
+        };
+
+        cout << "Part 1: " << dfs("you") << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+        auto graph = read_file("data/day11.txt");
+        part1(graph);
+}