1 files changed, 106 insertions, 0 deletions
diff --git a/2021/day12/day12.cpp b/2021/day12/day12.cpp
new file mode 100644
index 0000000..ab6a29e
--- /dev/null
+++ b/2021/day12/day12.cpp
@@ -0,0 +1,106 @@
+#include <iostream>
+#include <fstream>
+#include <string>
+#include <vector>
+#include <stack>
+#include "../utils.h"
+
+class Arc {
+	public: Arc (std::string s, std::string t) : s(s), t(t) {}
+	std::string s, t;
+};
+
+class Graph {
+	public: Graph () { }
+	std::vector<std::string> nodes;
+	std::vector<Arc> arcs;
+
+	std::vector<std::string> star (std::string start) {
+		std::vector<std::string> res;
+		for (auto arc : arcs) {
+			if (arc.s == start) res.push_back(arc.t);
+			if (arc.t == start) res.push_back(arc.s);
+		}
+		return res;
+	}
+};
+
+int count (std::vector<std::string> vec, std::string str) {
+	return std::count(std::begin(vec), std::end(vec), str);
+}
+
+bool lower (std::string str) {
+	for (auto c : str) if (!islower(c)) return false;
+	return true;
+}
+
+bool check (std::vector<std::string> vec, std::string str, bool twice) {
+	if (!lower(str)) return true;
+	if (count(vec, str) < 1) return true;
+	if (twice) {
+		std::string flag = "";
+		for (auto s : vec) {
+			if (count(vec, s) > 1 && lower(s)) {
+				if (flag == "") flag = s;
+				else return false;
+			}
+		}
+		return true;
+	}
+	return false;
+} 
+
+using Paths = std::vector<std::vector<std::string>>;
+Paths follow (Graph G, std::vector<std::string> path, bool twice) {
+	auto c = path[path.size()-1];
+	auto star = G.star(c);
+	Paths paths;
+	if (c == "end") {
+		paths.push_back(path);
+		return paths;
+	}
+	for (auto n : star) {
+		if (n == "start") continue;
+		if (!check(path, n, twice)) continue;
+
+		std::vector<std::string> newpath = path;
+		newpath.push_back(n);
+		Paths res = follow(G, newpath, twice);
+		paths.insert(std::end(paths), std::begin(res), std::end(res));
+	}
+	return paths;
+}
+
+Paths search (Graph G, bool twice) {
+	return follow(G, std::vector<std::string> { "start" }, twice);
+}
+
+
+int main (int argc, char *argv[]) {
+	std::string raw;
+	std::getline(std::ifstream(argv[1]), raw, '\0');
+	std::vector<std::string> lines;
+	split(lines, raw, "\n");
+	
+	Graph graph;
+	for (auto line : lines) {
+		if (line.size() == 0) continue; 
+		std::vector<std::string> tokens;
+		split(tokens, line, "-");
+		graph.nodes.push_back(tokens[0]);
+		graph.nodes.push_back(tokens[1]);
+		graph.arcs.push_back(Arc { tokens[0], tokens[1] });
+	}
+	
+	auto paths = search(graph, (argc > 2 ? (atoi(argv[2]) == 1) : false));
+	for (auto p : paths) {
+		for (auto s : p) {
+			std::cout << s << ",";
+		}
+		std::cout << std::endl;
+	}
+
+	std::cout << "paths: " << paths.size() << std::endl;
+
+	return 0;
+}