1 files changed, 80 insertions, 0 deletions

diff --git a/2016/src/day18.cpp b/2016/src/day18.cpp
new file mode 100644
index 0000000..66d1bf0
--- /dev/null
+++ b/2016/src/day18.cpp
@@ -0,0 +1,80 @@
+#include <algorithm>
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <string>
+
+using namespace std;
+
+namespace {
+
+string
+readFile(const filesystem::path& filename)
+{
+        ifstream file{ filename };
+        string   line;
+        getline(file, line);
+        return line;
+}
+
+void
+solve(string line, size_t lines)
+{
+        long count = 0;
+        while ( lines-- > 0 ) {
+                string current_line = "." + line + ".";
+
+                string new_line;
+
+                for ( size_t i = 1; i < current_line.size() - 1; ++i ) {
+                        auto next_chr = '.';
+
+                        const auto left   = current_line[i - 1];
+                        const auto middle = current_line[i];
+                        const auto right  = current_line[i + 1];
+
+                        if ( left == '^' && middle == '^' && right == '.' ) {
+                                next_chr = '^';
+                        }
+                        else if ( left == '.' && middle == '^' && right == '^' ) {
+                                next_chr = '^';
+                        }
+                        else if ( left == '^' && middle == '.' && right == '.' ) {
+                                next_chr = '^';
+                        }
+                        else if ( left == '.' && middle == '.' && right == '^' ) {
+                                next_chr = '^';
+                        }
+
+                        new_line += next_chr;
+                }
+
+                count += ranges::count(line, '.');
+
+                line = std::move(new_line);
+        }
+
+        cout << count << '\n';
+}
+
+void
+part1(const string& line)
+{
+        solve(line, 40);
+}
+
+void
+part2(const string& line)
+{
+        solve(line, 400000);
+}
+
+} // namespace
+
+int
+main()
+{
+        auto line = readFile("data/day18.txt");
+        part1(line);
+        part2(line);
+}