Add solution for "Day 19: Linen Layout", part 1

src/extra/LinenTowelPatterns.cpp

@@ -0,0 +1,101 @@
+// Solutions to the Advent Of Code 2024.
+// Copyright (C) 2025  Stefan Müller
+//
+// This program is free software: you can redistribute it and/or modify it under
+// the terms of the GNU General Public License as published by the Free Software
+// Foundation, either version 3 of the License, or (at your option) any later
+// version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along with
+// this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#include <aoc/extra/LinenTowelPatterns.hpp>
+
+#include <set>
+
+LinenTowelPatterns::LinenTowelPatterns()
+    : patterns_{}, stripes_{
+          { 'w', 0 },
+          { 'u', 1 },
+          { 'b', 2 },
+          { 'r', 3 },
+          { 'g', 4 }
+      }
+{
+    addBranch();
+}
+
+void LinenTowelPatterns::add(const std::string& towelPattern)
+{
+    size_t current{ 0 };
+    size_t next{ 0 };
+    for (const char stripe : towelPattern)
+    {
+        if (next >= patterns_.size())
+        {
+            patterns_[current].first = next;
+            addBranch();
+        }
+        current = next + stripes_[stripe];
+        next = patterns_[current].first > 0 ? patterns_[current].first : patterns_.size();
+    }
+    patterns_[current].second = true;
+}
+
+bool LinenTowelPatterns::isPossible(const std::string& design)
+{
+    std::vector<bool> canStartFrom(design.size(), false);
+    canStartFrom[0] = true;
+    std::set<size_t> unexploredStart;
+    unexploredStart.insert(0);
+
+    while (!unexploredStart.empty())
+    {
+        size_t designPosition = *unexploredStart.rbegin();
+        unexploredStart.erase(designPosition);
+
+        size_t i{ stripes_[design[designPosition]] };
+        while (++designPosition < design.size() && patterns_[i].first > 0)
+        {
+            if (patterns_[i].second && !canStartFrom[designPosition])
+            {
+                // The current accumulated stripe pattern exists and it ends at a new position within the design.
+                canStartFrom[designPosition] = true;
+                unexploredStart.insert(designPosition);
+            }
+            if (patterns_[i].first > 0)
+            {
+                // The current accumulated stripe pattern can be extended further.
+                i = patterns_[i].first + stripes_[design[designPosition]];
+            }
+        }
+        if (patterns_[i].second)
+        {
+            if (designPosition == design.size())
+            {
+                // The current accumulated stripe pattern exists and finishes the design.
+                return true;
+            }
+            else if (!canStartFrom[designPosition])
+            {
+                // The current accumulated stripe pattern exists and it ends at a new position within the design.
+                canStartFrom[designPosition] = true;
+                unexploredStart.insert(designPosition);
+            }
+        }
+    }
+
+    return false;
+}
+
+void LinenTowelPatterns::addBranch()
+{
+    for (size_t i = 0; i < stripes_.size(); i++)
+    {
+        patterns_.emplace_back(std::make_pair<size_t, bool>(0, false));
+    }
+}