Add solution for "Day 19: Linen Layout", part 2

include/aoc/extra/LinenTowelPatterns.hpp

@@ -24,9 +24,21 @@ class LinenTowelPatterns
 public:
     LinenTowelPatterns();
     void add(const std::string& towelPattern);
-    bool isPossible(const std::string& design);
+    int64_t countArrangements(const std::string& design);
 private:
+    /// <summary>
+    /// Tree data structure of all valid towel patterns. Each element is a vertex in the tree and represents a stripe in
+    /// a towel pattern given by 's = i mod n', where 's' is the unique index offset of the stripe as defined in
+    /// 'stripes_', 'i' is the index of the element, and 'n' is the number of stripes, i.e. the 'stripes_.size()'.
+    /// The first value of each element indicates the next set of stripes to continue the pattern accumulated by
+    /// following the path in the tree. If it is 0, this element is a leaf, and the pattern does not continue.
+    /// Otherwise, it is the index of its first of 'n' children, which are contiguous in the vector. The second value of
+    /// each element indicates whether there is a towel with the pattern ending at this element.
+    /// </summary>
     std::vector<std::pair<size_t, bool>> patterns_;
+    /// <summary>
+    /// Maps stripes (represented by chars) to an index offset in the tree of towel patterns.
+    /// </summary>
     std::map<char, size_t> stripes_;
     void addBranch();
 };