1 files changed, 110 insertions, 0 deletions

diff --git a/src/day08.cpp b/src/day08.cpp
new file mode 100644
index 0000000..3e1b6c9
--- /dev/null
+++ b/src/day08.cpp
@@ -0,0 +1,110 @@
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <regex>
+#include <numeric>
+using namespace std;
+
+struct Generator {
+        explicit Generator(string_view init)
+            : values_(init)
+            , iter_(values_.begin())
+
+        {
+        }
+
+        size_t next()
+        {
+                size_t gen = (*iter_ == 'L') ? 0 : 1;
+
+                ++iter_;
+                if ( iter_ == values_.end() ) {
+                        iter_ = values_.begin();
+                }
+
+                return gen;
+        }
+
+        string           values_;
+        string::iterator iter_;
+};
+
+void
+part1()
+{
+        fstream input{ "data/day08.txt" };
+
+        string line;
+        getline(input, line);
+
+        Generator generator{ line };
+
+        map<string, array<string, 2>> puzzle;
+
+        const regex pattern{ R"((.*) = \((.*), (.*)\))" };
+        while ( getline(input, line) ) {
+                if ( line.empty() ) {
+                        continue;
+                }
+
+                smatch sub_match;
+                if ( regex_search(line, sub_match, pattern) ) {
+                        puzzle[sub_match[1]] = { sub_match[2], sub_match[3] };
+                }
+        }
+
+        auto counter = 0;
+        for ( string str{ "AAA" }; str != "ZZZ"; str = puzzle[str][generator.next()] ) {
+                ++counter;
+        }
+        cout << counter << endl;
+}
+
+void
+part2()
+{
+        fstream input{ "data/day08.txt" };
+
+        string firstline;
+        getline(input, firstline);
+
+        map<string, array<string, 2>> puzzle;
+
+        const regex pattern{ R"((.*) = \((.*), (.*)\))" };
+        for ( string line; getline(input, line); ) {
+                if ( line.empty() ) {
+                        continue;
+                }
+
+                smatch sub_match;
+                if ( regex_search(line, sub_match, pattern) ) {
+                        puzzle[sub_match[1]] = { sub_match[2], sub_match[3] };
+                }
+        }
+
+        auto value = 1L;
+        for ( const auto& entry: puzzle ) {
+                if ( entry.first[2] != 'A' ) {
+                        continue;
+                }
+
+                Generator generator{ firstline };
+
+                auto counter = 0L;
+
+                for ( string str{ entry.first }; str[2] != 'Z'; str = puzzle[str][generator.next()] ) {
+                        ++counter;
+                }
+
+                value = lcm(value, counter);
+        }
+        cout << value << endl;
+}
+
+int
+main()
+{
+        part1();
+        part2();
+}