1 files changed, 91 insertions, 0 deletions
diff --git a/day12.cc b/day12.cc
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index 0000000..8d757eb
--- /dev/null
+++ b/day12.cc
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+#ifdef BOOST
+
+#include <iostream>
+#include <optional>
+
+// Using boost-1.65.1
+#include <boost/config.hpp>
+#include <boost/graph/adjacency_list.hpp>
+#include <boost/graph/connected_components.hpp>
+#include <boost/tokenizer.hpp>
+
+using namespace std;
+
+using undirected_graph =
+    boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS>;
+
+int
+main()
+{
+	undirected_graph G;
+
+	for (string line; getline(cin, line); ) {
+		optional<int> last;
+		for (string s : boost::tokenizer<>(line)) {
+			int i = stoi(s);
+			if (last)
+				add_edge(*last, i, G);
+			last = i;
+		}
+	}
+
+	vector<int> component(num_vertices(G));
+	int n = connected_components(G, &component[0]);
+	cout << count(begin(component), end(component), component[0]) << endl;
+	cout << n << endl;
+}
+
+// 134
+// 193
+
+#else //////////////////////////////////////////////////////////////////////
+
+#include <algorithm>
+#include <deque>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+// bfs approach without recursion
+// adapted from https://www.reddit.com/r/adventofcode/comments/7j89tr/x/dr4iya8/
+
+int main()
+{
+	vector<vector<int>> edges;
+
+	for (string line; getline(cin, line); ) {		
+		istringstream line_stream{line};
+		int vertex_a, vertex_b;
+		string _;
+		line_stream >> vertex_a >> _;
+		for (edges.emplace_back();  // assumes lines arrive in order
+		     line_stream >> vertex_b;
+		     line_stream >> _)
+			edges[vertex_a].emplace_back(vertex_b);
+	}
+
+	vector<int> comp(size(edges), -1);
+	int n = 0;
+
+	for (auto vertex = begin(comp);
+	     vertex != end(comp);
+	     ++n, vertex = find(begin(comp), end(comp), -1)) {
+		deque<long> queue{distance(begin(comp), vertex)};
+		while (!empty(queue)) {
+			int v = queue.front();
+			queue.pop_front();
+			comp[v] = n;
+			copy_if(begin(edges[v]), end(edges[v]),
+			    back_inserter(queue),
+			    [&](int v){ return comp[v] == -1; });
+		}
+	}
+
+	cout << count(begin(comp), end(comp), 0) << endl;
+	cout << n << endl;
+}
+
+#endif