Add solution for "Day 21: Keypad Conundrum", part 1

src/extra/KeypadRobot.cpp

@@ -0,0 +1,68 @@
+// 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/KeypadRobot.hpp>
+
+#include <sstream>
+
+KeypadRobot::KeypadRobot(const std::map<char, Point2>&& keypad, const Point2&& forbidden)
+    : keypad_{ keypad }, forbidden_{ forbidden }
+{
+}
+
+std::string KeypadRobot::calcInputKeys(const std::string& targetOutputKeys) const
+{
+    std::ostringstream stream{};
+    Point2 position{ 0, 0 };
+    for (const char c : targetOutputKeys)
+    {
+        Point2 next = keypad_.at(c);
+
+        // This specific order of robot arm movements aims to reduce resulting combinations of 'A' and '<' for the
+        // second robot, which expand to more key presses starting with the third robot.
+        bool horizontalFirst{ (next.x < position.x && !(next.x == forbidden_.x && position.y == forbidden_.y)) ||
+            (position.x == forbidden_.x && next.y == forbidden_.y) };
+        if (horizontalFirst)
+        {
+            move(stream, next.x - position.x, '>', '<');
+        }
+        move(stream, next.y - position.y, 'v', '^');
+        if (!horizontalFirst)
+        {
+            move(stream, next.x - position.x, '>', '<');
+        }
+        stream << 'A';
+        position = next;
+    }
+    return stream.str();
+}
+
+void KeypadRobot::move(std::ostringstream& stream, const int delta, const char positive, const char negative) const
+{
+    if (delta > 0)
+    {
+        for (int i{ 0 }; i < delta; i++)
+        {
+            stream << positive;
+        }
+    }
+    else
+    {
+        for (int i{ 0 }; i < -delta; i++)
+        {
+            stream << negative;
+        }
+    }
+}