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| Original file line number | Diff line number | Diff line change |
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| /* | ||
| * BSD Zero Clause License | ||
| * | ||
| * Copyright (c) 2021-2024 zodac.me | ||
| * | ||
| * Permission to use, copy, modify, and/or distribute this software for any | ||
| * purpose with or without fee is hereby granted. | ||
| * | ||
| * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES | ||
| * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF | ||
| * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY | ||
| * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES | ||
| * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN | ||
| * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR | ||
| * IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. | ||
| */ | ||
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| package me.zodac.advent; | ||
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| import java.util.List; | ||
| import java.util.Set; | ||
| import java.util.function.BiPredicate; | ||
| import me.zodac.advent.grid.AdjacentDirection; | ||
| import me.zodac.advent.grid.Grid; | ||
| import me.zodac.advent.grid.GridFactory; | ||
| import me.zodac.advent.pojo.Point; | ||
| import me.zodac.advent.search.PathFinder; | ||
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| /** | ||
| * Solution for 2024, Day 18. | ||
| * | ||
| * @see <a href="https://adventofcode.com/2024/day/18">[2024: 18] RAM Run</a> | ||
| */ | ||
| public final class Day18 { | ||
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| private static final char OBSTACLE_SYMBOL = '#'; | ||
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| private Day18() { | ||
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| } | ||
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| /** | ||
| * Creates a {@link Grid} populated with obstacles defined by the input {@link Point}s. While many {@link Point}s are provided, only | ||
| * {@code pointsToCheck} {@link Point}s should be considered. | ||
| * | ||
| * <p> | ||
| * Once the obstacles have been populated, find the shortest path between the top-left {@link Point} to the bottom-right {@link Point}. Return | ||
| * the number of steps required (size of path - <b>1</b>). | ||
| * | ||
| * @param obstaclePoints the input {@link Point}s defining the obstacles on the {@link Grid} | ||
| * @param gridSize the size of the {@link Grid} | ||
| * @param pointsToCheck the number of obstacle {@link Point}s to consider | ||
| * @return the smallest number of steps between the start and end {@link Point} | ||
| */ | ||
| public static long smallestStepsBetweenStartAndEnd(final List<Point> obstaclePoints, final int gridSize, final int pointsToCheck) { | ||
| final Point startPoint = Point.atOrigin(); | ||
| final Point endPoint = Point.of(gridSize - 1, gridSize - 1); | ||
| final Grid<Character> grid = createPopulatedGrid(obstaclePoints, gridSize, pointsToCheck); | ||
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| // Ignore first point, since we're looking for number of steps | ||
| final BiPredicate<Point, Point> filter = (_, nextPoint) -> grid.at(nextPoint) != OBSTACLE_SYMBOL; | ||
| return PathFinder.shortest(grid, startPoint, endPoint, AdjacentDirection.CARDINAL, filter).size() - 1; | ||
| } | ||
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| /** | ||
| * Having previously found the shortest path from start {@link Point} to end {@link Point}, we continue adding obstacles from the input | ||
| * {@link Point}s supplied. We can start from a later index, defined by {@code previouslyCheckedPoints} to speed up our analysis. | ||
| * | ||
| * <p> | ||
| * We keep adding new {@link Point}s until we find one that prevents any valid path between the start {@link Point} and the end {@link Point}. We | ||
| * then return this {@link Point} as a {@link String} in the format: | ||
| * <pre> | ||
| * x,y | ||
| * </pre> | ||
| * | ||
| * @param obstaclePoints the input {@link Point}s defining the obstacles on the {@link Grid} | ||
| * @param gridSize the size of the {@link Grid} | ||
| * @param previouslyCheckedPoints the starting value to continue checking subsequent {@link Point}s | ||
| * @return the {@link Point} that blocks the start {@link Point} from the end {@link Point}, as a {@link String} | ||
| */ | ||
| public static String findPointWhichBlocksPath(final List<Point> obstaclePoints, final int gridSize, final int previouslyCheckedPoints) { | ||
| final Point startPoint = Point.atOrigin(); | ||
| final Point endPoint = Point.of(gridSize - 1, gridSize - 1); | ||
| Grid<Character> grid = createPopulatedGrid(obstaclePoints, gridSize, previouslyCheckedPoints); | ||
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| for (int i = previouslyCheckedPoints; i <= obstaclePoints.size(); i++) { | ||
| final Point point = obstaclePoints.get(i); | ||
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| grid = grid.updateAt(point, OBSTACLE_SYMBOL); | ||
| final Grid<Character> updatedGrid = grid; // Stupid workaround for lambda function | ||
| final BiPredicate<Point, Point> filter = (_, nextPoint) -> updatedGrid.at(nextPoint) != OBSTACLE_SYMBOL; | ||
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| final Set<Point> shortestPath = PathFinder.shortest(updatedGrid, startPoint, endPoint, AdjacentDirection.CARDINAL, filter); | ||
| if (shortestPath.isEmpty()) { | ||
| return String.format("%s,%s", point.x(), point.y()); | ||
| } | ||
| } | ||
| throw new IllegalStateException("Unable to find any Point to block the path"); | ||
| } | ||
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| private static Grid<Character> createPopulatedGrid(final List<Point> values, final int gridSize, final int bytesToCheck) { | ||
| Grid<Character> grid = GridFactory.ofCharactersWithSize(gridSize); | ||
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| for (int i = 0; i < bytesToCheck; i++) { | ||
| final Point point = values.get(i); | ||
| grid = grid.updateAt(point, OBSTACLE_SYMBOL); | ||
| } | ||
| return grid; | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,77 @@ | ||
| /* | ||
| * BSD Zero Clause License | ||
| * | ||
| * Copyright (c) 2021-2024 zodac.me | ||
| * | ||
| * Permission to use, copy, modify, and/or distribute this software for any | ||
| * purpose with or without fee is hereby granted. | ||
| * | ||
| * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES | ||
| * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF | ||
| * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY | ||
| * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES | ||
| * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN | ||
| * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR | ||
| * IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. | ||
| */ | ||
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| package me.zodac.advent; | ||
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| import static org.assertj.core.api.Assertions.assertThat; | ||
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| import java.util.List; | ||
| import me.zodac.advent.input.InputReader; | ||
| import me.zodac.advent.pojo.Point; | ||
| import org.junit.jupiter.api.Test; | ||
|
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| /** | ||
| * Tests to verify answers for {@link Day18}. | ||
| */ | ||
| class Day18Test { | ||
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| private static final String INPUT_FILENAME = "day18.txt"; | ||
| private static final int GRID_SIZE_EXAMPLE = 7; | ||
| private static final int GRID_SIZE_PUZZLE = 71; | ||
| private static final int POINTS_TO_CHECK_EXAMPLE = 12; | ||
| private static final int POINTS_TO_CHECK_PUZZLE = 1024; | ||
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| @Test | ||
| void example() { | ||
| final List<Point> values = InputReader | ||
| .forExample(INPUT_FILENAME) | ||
| .as(Point::parse) | ||
| .readAllLines(); | ||
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| final long part1Result = Day18.smallestStepsBetweenStartAndEnd(values, GRID_SIZE_EXAMPLE, POINTS_TO_CHECK_EXAMPLE); | ||
| assertThat(part1Result) | ||
| .isEqualTo(22L); | ||
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| final String part2Result = Day18.findPointWhichBlocksPath(values, GRID_SIZE_EXAMPLE, POINTS_TO_CHECK_EXAMPLE); | ||
| assertThat(part2Result) | ||
| .isEqualTo("6,1"); | ||
| } | ||
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| @Test | ||
| void part1() { | ||
| final List<Point> values = InputReader | ||
| .forPuzzle(INPUT_FILENAME) | ||
| .as(Point::parse) | ||
| .readAllLines(); | ||
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| final long part1Result = Day18.smallestStepsBetweenStartAndEnd(values, GRID_SIZE_PUZZLE, POINTS_TO_CHECK_PUZZLE); | ||
| assertThat(part1Result) | ||
| .isEqualTo(278L); | ||
| } | ||
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| @Test | ||
| void part2() { | ||
| final List<Point> values = InputReader | ||
| .forPuzzle(INPUT_FILENAME) | ||
| .as(Point::parse) | ||
| .readAllLines(); | ||
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| final String part2Result = Day18.findPointWhichBlocksPath(values, GRID_SIZE_PUZZLE, POINTS_TO_CHECK_PUZZLE); | ||
| assertThat(part2Result) | ||
| .isEqualTo("43,12"); | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,25 @@ | ||
| 5,4 | ||
| 4,2 | ||
| 4,5 | ||
| 3,0 | ||
| 2,1 | ||
| 6,3 | ||
| 2,4 | ||
| 1,5 | ||
| 0,6 | ||
| 3,3 | ||
| 2,6 | ||
| 5,1 | ||
| 1,2 | ||
| 5,5 | ||
| 2,5 | ||
| 6,5 | ||
| 1,4 | ||
| 0,4 | ||
| 6,4 | ||
| 1,1 | ||
| 6,1 | ||
| 1,0 | ||
| 0,5 | ||
| 1,6 | ||
| 2,0 |
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Submodule advent-of-code-inputs
updated
from 2fea4b to b9bd7d
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