1 files changed, 89 insertions, 0 deletions

diff --git a/2016/src/day15.cpp b/2016/src/day15.cpp
new file mode 100644
index 0000000..ced6102
--- /dev/null
+++ b/2016/src/day15.cpp
@@ -0,0 +1,89 @@
+#include <algorithm>
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <regex>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+struct Disc {
+        [[nodiscard]]
+        bool zeroAtTime(int time) const
+        {
+                return (time + num + phase) % positions == 0;
+        }
+
+        int num;
+        int phase;
+        int positions;
+};
+
+vector<int>
+extractNumbers(const string& text)
+{
+        static const regex number_regex("\\d+");
+
+        vector<int> numbers;
+        smatch      match;
+
+        auto searchStart = text.cbegin();
+        while ( regex_search(searchStart, text.cend(), match, number_regex) ) {
+                numbers.emplace_back(stoi(match.str()));
+                searchStart = match.suffix().first;
+        }
+
+        return numbers;
+}
+
+vector<Disc>
+readFile(const filesystem::path& filename)
+{
+        ifstream     file{ filename };
+        vector<Disc> discs;
+
+        for ( string line; getline(file, line); ) {
+                auto numbers = extractNumbers(line);
+                discs.emplace_back(numbers.at(0), numbers.at(3), numbers.at(1));
+        }
+
+        return discs;
+}
+
+void
+solve(const vector<Disc>& discs)
+{
+        for ( int time = 0;; ++time ) {
+                auto found = ranges::all_of(discs, [&time](const auto& disc) { return disc.zeroAtTime(time); });
+                if ( found ) {
+                        cout << time << '\n';
+                        return;
+                }
+        }
+}
+
+void
+part1(const vector<Disc>& discs)
+{
+        solve(discs);
+}
+
+void
+part2(vector<Disc> discs)
+{
+        discs.emplace_back(discs.size() + 1, 0, 11);
+        solve(discs);
+}
+
+} // namespace
+
+int
+main()
+{
+        auto discs = readFile("data/day15.txt");
+        part1(discs);
+        part2(discs);
+}