Add solution for "Day 15: Warehouse Woes", part 2

README.md

@@ -98,6 +98,14 @@ For part 1, the resulting quadrant for each robot can be calculated directly, by
 
 When observing a few resulting robot configurations after each passed second, it becomes apparent that some of them show vertical or horizontal bands of clustering, and that these repeat every `width` or `height` seconds, respectively. With a bit of modulo calculus, the time after which the vertical and horizontal bands overlap can be determined, which is the solution for part 2.
 
+### Day 15: Warehouse Woes
+
+:mag_right: Puzzle: <https://adventofcode.com/2024/day/15>, :white_check_mark: Solver: [`WarehouseWoes.cpp`](src/WarehouseWoes.cpp)
+
+The idea for this solver was pretty straight forward. The algorithm moves the robot around the warehouse following the instructions, and checks whether boxes in its way can be pushed, that is whether there is an empty spot behind the box, or stack of boxes.
+
+It is more complicated for part 2 of course, since here horizontal and vertical directions behave differently. For vertical pushes there are two phases, the first one where individual boxes to be pushed are found, tracked, and checked for walls behind them, and a second phase where all those boxes are moved in reverse order.
+
 ## Thanks
 
 * [Alexander Brouwer](https://github.com/Bromvlieg) for getting the project set up with CMake.

include/aoc/WarehouseBoxPusher.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 <string>
+#include <vector>
+
+#include <aoc/Lines.hpp>
+#include <aoc/Point2.hpp>
+
+class WarehouseBoxPusher
+{
+public:
+    WarehouseBoxPusher(const char boxChar, const char wallChar, const char emptyChar);
+    virtual ~WarehouseBoxPusher(){};
+    virtual void processMovements(Lines& warehouseMap, const std::string& line);
+    virtual void processMovement(Lines& warehouseMap, const Point2& direction);
+    void setRobotPosition(const Point2& robotPosition);
+protected:
+    Point2 robotPosition_;
+    const char boxChar_;
+    const char wallChar_;
+    const char emptyChar_;
+};

include/aoc/WarehouseWideBoxPusher.hpp

@@ -0,0 +1,30 @@
+// 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/WarehouseBoxPusher.hpp>
+
+class WarehouseWideBoxPusher
+    : public WarehouseBoxPusher
+{
+public:
+    WarehouseWideBoxPusher(const char leftWideBoxChar, const char rightWideBoxChar, const char wallChar,
+        const char emptyChar);
+    virtual void processMovement(Lines& warehouseMap, const Point2& direction) override;
+protected:
+    const char leftWideBoxChar_;
+    const char rightWideBoxChar_;
+};

include/aoc/WarehouseWoes.hpp

@@ -15,7 +15,10 @@
 
 #pragma once
 
+#include <aoc/Lines.hpp>
 #include <aoc/LinesSolver.hpp>
+#include <aoc/WarehouseBoxPusher.hpp>
+#include <aoc/WarehouseWideBoxPusher.hpp>
 
 class WarehouseWoes
     : public LinesSolver
@@ -28,11 +31,18 @@ class WarehouseWoes
     virtual void finish() override;
 private:
     bool isProcessingMap_;
-    Point2 robotPosition_;
+    bool isSearchingStartPosition_;
+    Lines lines2_;
+    WarehouseBoxPusher warehouseBoxPusher1_;
+    WarehouseWideBoxPusher warehouseBoxPusher2_;
     static constexpr char getRobotChar();
     static constexpr char getBoxChar();
+    static constexpr char getLeftWideBoxChar();
+    static constexpr char getRightWideBoxChar();
     static constexpr char getWallChar();
     static constexpr char getEmptyChar();
-    void processDirections(const std::string& line);
-    int calcGpsCoordinate(const size_t x, const size_t y);
+    void checkStartingPosition(const std::string& line);
+    void addWarehouseMap2Line(const std::string& line);
+    long long int calcAllGpsCoordinates(Lines& warehouseMap, const char boxChar);
+    long long int calcGpsCoordinate(const size_t x, const size_t y);
 };

src/WarehouseBoxPusher.cpp

@@ -0,0 +1,53 @@
+// 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/WarehouseBoxPusher.hpp>
+
+WarehouseBoxPusher::WarehouseBoxPusher(const char boxChar, const char wallChar, const char emptyChar)
+    : boxChar_{ boxChar }, wallChar_{ wallChar }, emptyChar_{ emptyChar }
+{
+}
+
+void WarehouseBoxPusher::processMovements(Lines& warehouseMap, const std::string& line)
+{
+    for (const char c : line)
+    {
+        processMovement(warehouseMap, Point2::getCardinalDirection(c));
+    }
+}
+
+void WarehouseBoxPusher::processMovement(Lines& warehouseMap, const Point2& direction)
+{
+    const Point2 next{ robotPosition_ + direction };
+    Point2 push{ next };
+    while (warehouseMap.getCharAt(push) == boxChar_)
+    {
+        push += direction;
+    }
+    if (warehouseMap.getCharAt(push) != wallChar_)
+    {
+        if (push != next)
+        {
+            warehouseMap.setCharAt(push, boxChar_);
+            warehouseMap.setCharAt(next, emptyChar_);
+        }
+        robotPosition_ = next;
+    }
+}
+
+void WarehouseBoxPusher::setRobotPosition(const Point2& robotPosition)
+{
+    robotPosition_ = robotPosition;
+}

src/WarehouseWideBoxPusher.cpp

@@ -0,0 +1,130 @@
+// 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/WarehouseWideBoxPusher.hpp>
+
+#include <stack>
+
+WarehouseWideBoxPusher::WarehouseWideBoxPusher(const char leftWideBoxChar, const char rightWideBoxChar,
+    const char wallChar, const char emptyChar)
+    : WarehouseBoxPusher{ 0, wallChar, emptyChar }, leftWideBoxChar_{ leftWideBoxChar },
+      rightWideBoxChar_{ rightWideBoxChar }
+{
+}
+
+void WarehouseWideBoxPusher::processMovement(Lines& warehouseMap, const Point2& direction)
+{
+    const Point2 next{ robotPosition_ + direction };
+
+    if (direction.y == 0)
+    {
+        // Moves robot horizontally.
+        const char facingBoxChar = direction.x > 0 ? leftWideBoxChar_ : rightWideBoxChar_;
+        const Point2 doubleDirection{ direction.x * 2, 0 };
+        Point2 push{ next };
+        while (warehouseMap.getCharAt(push) == facingBoxChar)
+        {
+            push += doubleDirection;
+        }
+        if (warehouseMap.getCharAt(push) != wallChar_)
+        {
+            if (push != next)
+            {
+                auto& line = warehouseMap[next.y];
+                line.erase(line.begin() + push.x);
+                line.insert(line.begin() + next.x, emptyChar_);
+            }
+            robotPosition_ = next;
+        }
+    }
+    else
+    {
+        // Moves robot vertically.
+
+        // Checks if a wall is blocking the movement directly in front of the robot.
+        const char charToCheck{ warehouseMap.getCharAt(next) };
+        if (charToCheck == wallChar_)
+        {
+            return;
+        }
+
+        bool canPush{ true };
+        std::vector<Point2> boxesToPush{};
+        std::stack<Point2> boxesToCheck{};
+
+        // Checks for the first box to push and stacks its left position, if any.
+        if (charToCheck == leftWideBoxChar_)
+        {
+            boxesToCheck.push(next);
+        }
+        else if (charToCheck == rightWideBoxChar_)
+        {
+            boxesToCheck.emplace(next.x - 1, next.y);
+        }
+
+        // Checks all pushed boxes.
+        while (!boxesToCheck.empty())
+        {
+            Point2 leftPush{ boxesToCheck.top() };
+            boxesToCheck.pop();
+
+            // Checks whether any wall is blocking the push.
+            Point2 rightPush{ leftPush + Point2::right };
+            const char leftCharToCheck{ warehouseMap.getCharAt(leftPush) };
+            const char rightCharToCheck{ warehouseMap.getCharAt(rightPush) };
+            if (leftCharToCheck == wallChar_ || rightCharToCheck == wallChar_)
+            {
+                canPush = false;
+                break;
+            }
+
+            // Checks if any more boxes are being pushed by this box.
+            if (leftCharToCheck == leftWideBoxChar_)
+            {
+                boxesToPush.push_back(leftPush);
+                boxesToCheck.emplace(leftPush.x, leftPush.y + direction.y);
+            }
+            else
+            {
+                if (leftCharToCheck == rightWideBoxChar_)
+                {
+                    leftPush += Point2::left;
+                    boxesToPush.push_back(leftPush);
+                    boxesToCheck.emplace(leftPush.x, leftPush.y + direction.y);
+                }
+                if (rightCharToCheck == leftWideBoxChar_)
+                {
+                    boxesToPush.push_back(rightPush);
+                    boxesToCheck.emplace(rightPush.x, rightPush.y + direction.y);
+                }
+            }
+        }
+
+        if (canPush)
+        {
+            // Moves all pushed boxes.
+            auto it = boxesToPush.crbegin();
+            while (it != boxesToPush.crend())
+            {
+                warehouseMap.setCharAt(*it, emptyChar_);
+                warehouseMap.setCharAt(*it + Point2::right, emptyChar_);
+                warehouseMap.setCharAt(*it + direction, leftWideBoxChar_);
+                warehouseMap.setCharAt(*it + direction + Point2::right, rightWideBoxChar_);
+                it++;
+            }
+            robotPosition_ = next;
+        }
+    }
+}

src/WarehouseWoes.cpp

@@ -15,8 +15,12 @@
 
 #include <aoc/WarehouseWoes.hpp>
 
+#include <sstream>
+
 WarehouseWoes::WarehouseWoes(const int inputFileNameSuffix)
-    : LinesSolver{ inputFileNameSuffix }, isProcessingMap_{ true }, robotPosition_{}
+    : LinesSolver{ inputFileNameSuffix }, isProcessingMap_{ true }, isSearchingStartPosition_{ true }, lines2_{},
+      warehouseBoxPusher1_{ getBoxChar(), getWallChar(), getEmptyChar() },
+      warehouseBoxPusher2_{ getLeftWideBoxChar(), getRightWideBoxChar(), getWallChar(), getEmptyChar() }
 {
 }
 
@@ -36,16 +40,14 @@ void WarehouseWoes::processDataLine(const std::string& line)
     {
         if (isProcessingMap_)
         {
-            auto hit = line.find(getRobotChar());
-            if (hit != std::string::npos)
-            {
-                robotPosition_ = { static_cast<int>(hit), static_cast<int>(lines.size()) };
-            }
+            checkStartingPosition(line);
             LinesSolver::processDataLine(line);
+            addWarehouseMap2Line(line);
         }
         else
         {
-            processDirections(line);
+            warehouseBoxPusher1_.processMovements(lines, line);
+            warehouseBoxPusher2_.processMovements(lines2_, line);
         }
     }
     else
@@ -56,16 +58,8 @@ void WarehouseWoes::processDataLine(const std::string& line)
 
 void WarehouseWoes::finish()
 {
-    for (size_t j = 0; j < lines.size(); j++)
-    {
-        for (size_t i = 0; i < lines[j].size(); i++)
-        {
-            if (lines[j][i] == getBoxChar())
-            {
-                part1 += calcGpsCoordinate(i, j);
-            }
-        }
-    }
+    part1 = calcAllGpsCoordinates(lines, getBoxChar());
+    part2 = calcAllGpsCoordinates(lines2_, getLeftWideBoxChar());
 }
 
 constexpr char WarehouseWoes::getRobotChar()
@@ -78,6 +72,16 @@ constexpr char WarehouseWoes::getBoxChar()
     return 'O';
 }
 
+constexpr char WarehouseWoes::getLeftWideBoxChar()
+{
+    return '[';
+}
+
+constexpr char WarehouseWoes::getRightWideBoxChar()
+{
+    return ']';
+}
+
 constexpr char WarehouseWoes::getWallChar()
 {
     return '#';
@@ -88,27 +92,56 @@ constexpr char WarehouseWoes::getEmptyChar()
     return '.';
 }
 
-void WarehouseWoes::processDirections(const std::string& line)
+void WarehouseWoes::checkStartingPosition(const std::string& line)
 {
-    for (const char c : line)
+    if (isSearchingStartPosition_)
     {
-        const Point2 direction{ Point2::getCardinalDirection(c) };
-        const Point2 next{ robotPosition_ + direction };
-        Point2 push{ next };
-        while (getCharAt(push) == getBoxChar())
+        auto hit = line.find(getRobotChar());
+        if (hit != std::string::npos)
         {
-            push += direction;
-        }
-        if (getCharAt(push) != getWallChar())
-        {
-            setCharAt(push, getBoxChar());
-            setCharAt(next, getEmptyChar());
-            robotPosition_ = next;
+            int x = static_cast<int>(hit);
+            int y = static_cast<int>(lines.size());
+            warehouseBoxPusher1_.setRobotPosition({ x, y });
+            warehouseBoxPusher2_.setRobotPosition({ x * 2, y });
+            isSearchingStartPosition_ = false;
         }
     }
 }
 
-int WarehouseWoes::calcGpsCoordinate(const size_t x, const size_t y)
+void WarehouseWoes::addWarehouseMap2Line(const std::string& line)
+{
+    std::ostringstream stream{};
+    for (const char c : line)
+    {
+        if (c == getBoxChar())
+        {
+            stream << getLeftWideBoxChar() << getRightWideBoxChar();
+        }
+        else
+        {
+            stream << c << c;
+        }
+    }
+    lines2_.push_back(stream.str());
+}
+
+long long int WarehouseWoes::calcAllGpsCoordinates(Lines& warehouseMap, const char boxChar)
+{
+    long long int result{ 0 };
+    for (size_t j = 0; j < warehouseMap.size(); j++)
+    {
+        for (size_t i = 0; i < warehouseMap[j].size(); i++)
+        {
+            if (warehouseMap[j][i] == boxChar)
+            {
+                result += calcGpsCoordinate(i, j);
+            }
+        }
+    }
+    return result;
+}
+
+long long int WarehouseWoes::calcGpsCoordinate(const size_t x, const size_t y)
 {
     return x + 100 * y;
 }

tests/src/TestCases.cpp

@@ -240,15 +240,15 @@ TEST_CASE("[WarehouseWoesTests]")
     TestContext test;
     SECTION("FullData")
     {
-        test.run(std::make_unique<WarehouseWoes>(), 1515788, 0, test.getInputPaths());
+        test.run(std::make_unique<WarehouseWoes>(), 1515788, 1516544, test.getInputPaths());
     }
     SECTION("ExampleData")
     {
-        test.run(std::make_unique<WarehouseWoes>(), 10092, 0, test.getExampleInputPaths());
+        test.run(std::make_unique<WarehouseWoes>(), 10092, 9021, test.getExampleInputPaths());
     }
     SECTION("ExampleData2")
     {
-        test.run(std::make_unique<WarehouseWoes>(2), 2028, 0, test.getExampleInputPaths());
+        test.runPart1(std::make_unique<WarehouseWoes>(2), 2028, test.getExampleInputPaths());
     }
 }