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

include/aoc/KeypadConundrum.hpp

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+// 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/>.
+
+#pragma once
+
+#include <aoc/extra/KeypadRobot.hpp>
+#include <aoc/framework/Solver-types.hpp>
+
+class KeypadConundrum
+    : public Solver<int64_t, int64_t>
+{
+public:
+    KeypadConundrum();
+    virtual const std::string getPuzzleName() const override;
+    virtual const int getPuzzleDay() const override;
+    virtual void processDataLine(const std::string& line) override;
+    virtual void finish() override;
+private:
+    static constexpr char getStartPositionChar();
+    KeypadRobot numericKeyboardRobot_;
+    KeypadRobot directionalKeyboardRobot_;
+};

include/aoc/extra/KeypadRobot.hpp

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+// 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/>.
+
+#pragma once
+
+#include <map>
+#include <string>
+
+#include <aoc/common/Point2.hpp>
+
+class KeypadRobot
+{
+public:
+    KeypadRobot(const std::map<char, Point2>&& keypad, const Point2&& forbidden);
+    std::string calcInputKeys(const std::string& targetOutputKeys) const;
+private:
+    const std::map<char, Point2> keypad_;
+    const Point2 forbidden_;
+    void move(std::ostringstream& stream, const int delta, const char positive, const char negative) const;
+};