Add solution for "Day 20: Race Condition", part 1

include/aoc/RaceCondition.hpp

@@ -0,0 +1,37 @@
+// 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/common/Grid.hpp>
+#include <aoc/framework/LinesSolver.hpp>
+
+class RaceCondition
+    : public LinesSolver<int64_t, int64_t>
+{
+public:
+    RaceCondition(const int threshold = 100);
+    virtual const std::string getPuzzleName() const override;
+    virtual const int getPuzzleDay() const override;
+    virtual void finish() override;
+private:
+    static constexpr char getStartChar();
+    static constexpr char getWallChar();
+    static constexpr int getCheatLength();
+    const std::array<Point2, 8> doubleSteps_{ Point2::down * 2, Point2::downRight, Point2::right * 2,
+        Point2::upRight, Point2::up * 2, Point2::upLeft, Point2::left * 2, Point2::downLeft };
+    int threshold_;
+    void checkCheat(const Point2& position, Grid<int>& times);
+};

src/Program.cpp

@@ -40,6 +40,7 @@
 #include <aoc/ChronospatialComputer.hpp>
 #include <aoc/RamRun.hpp>
 #include <aoc/LinenLayout.hpp>
+#include <aoc/RaceCondition.hpp>
 #include <aoc/LanParty.hpp>
 
 void Program::run()
@@ -77,6 +78,7 @@ void Program::runSolvers()
     runSolver<ChronospatialComputer>(solverEngine);
     runSolver<RamRun>(solverEngine);
     runSolver<LinenLayout>(solverEngine);
+    runSolver<RaceCondition>(solverEngine);
     runSolver<LanParty>(solverEngine);
 }
 

src/RaceCondition.cpp

@@ -0,0 +1,91 @@
+// 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/RaceCondition.hpp>
+
+RaceCondition::RaceCondition(const int threshold)
+    : threshold_{ threshold }
+{
+}
+
+const std::string RaceCondition::getPuzzleName() const
+{
+    return "Race Condition";
+}
+
+const int RaceCondition::getPuzzleDay() const
+{
+    return 20;
+}
+
+void RaceCondition::finish()
+{
+    int time{ 0 };
+    Grid<int> times{ lines.size(), lines[0].size() };
+    // Fills the grid with a number that is guaranteed to be greater than the length of the path.
+    times.fill(static_cast<int>(times.getNColumns() * times.getNRows()));
+
+    Point2 position{ findChar(getStartChar()) };
+    Point2 previous{ -1, -1 };
+    while (position != previous)
+    {
+        // Tracks time for current position.
+        times.cell(position) = time++;
+
+        // Checks if there is a cheat leading to the current position.
+        checkCheat(position, times);
+
+        // Progresses the race path.
+        auto oldPosition = position;
+        for (const auto& direction : Point2::cardinalDirections)
+        {
+            auto next = position + direction;
+            if (next != previous && getCharAt(next) != getWallChar())
+            {
+                position = next;
+                break;
+            }
+        }
+        previous = oldPosition;
+    }
+}
+
+constexpr char RaceCondition::getStartChar()
+{
+    return 'S';
+}
+
+constexpr char RaceCondition::getWallChar()
+{
+    return '#';
+}
+
+constexpr int RaceCondition::getCheatLength()
+{
+    return 2;
+}
+
+void RaceCondition::checkCheat(const Point2& position, Grid<int>& times)
+{
+    auto time = times.cell(position);
+    for (auto& direction : doubleSteps_)
+    {
+        auto other = position + direction;
+        if (isInBounds(other) && time >= threshold_ + times.cell(other) + getCheatLength())
+        {
+            part1++;
+        }
+    }
+}

tests/src/TestCases.cpp

@@ -37,6 +37,7 @@
 #include <aoc/ChronospatialComputer.hpp>
 #include <aoc/RamRun.hpp>
 #include <aoc/LinenLayout.hpp>
+#include <aoc/RaceCondition.hpp>
 #include <aoc/LanParty.hpp>
 
 #define REQUIRE_MESSAGE(cond, msg) if (!(cond)) { INFO(msg); REQUIRE(cond); }
@@ -354,6 +355,19 @@ TEST_CASE("[LinenLayoutTests]")
     }
 }
 
+TEST_CASE("[RaceConditionTests]")
+{
+    TestContext test;
+    SECTION("FullData")
+    {
+        test.runFull(std::make_unique<RaceCondition>(), 1448, 0);
+    }
+    SECTION("ExampleData")
+    {
+        test.runExample(std::make_unique<RaceCondition>(2), 44, 0);
+    }
+}
+
 TEST_CASE("[LanPartyTests]")
 {
     TestContext test;