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166 changes: 155 additions & 11 deletions
166
adventofcode/src/main/java/org/ck/adventofcode/year2024/Day20.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,34 +1,178 @@ | ||
| package org.ck.adventofcode.year2024; | ||
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| import java.util.Scanner; | ||
| import java.util.*; | ||
| import org.ck.adventofcode.util.AOCSolution; | ||
| import org.ck.codechallengelib.annotation.Solution; | ||
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| @Solution( | ||
| id = 20242001, | ||
| name = "Day 20: ?", | ||
| name = "Day 20: Race Condition", | ||
| url = "https://adventofcode.com/2024/day/20", | ||
| category = "2024", | ||
| solved = false) | ||
| category = "2024") | ||
| @Solution( | ||
| id = 20242002, | ||
| name = "Day 20: ? - Part 2", | ||
| name = "Day 20: Race Condition - Part 2", | ||
| url = "https://adventofcode.com/2024/day/20#part2", | ||
| category = "2024", | ||
| solved = false) | ||
| category = "2024") | ||
| public class Day20 extends AOCSolution { | ||
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| @Override | ||
| protected void runPartOne(final Scanner in) { | ||
| run(in); | ||
| run(in, 2); | ||
| } | ||
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| @Override | ||
| protected void runPartTwo(final Scanner in) { | ||
| run(in); | ||
| run(in, 20); | ||
| } | ||
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| private void run(final Scanner in) { | ||
| print("Whoopsie"); | ||
| private void run(final Scanner in, final int allowedCheatTime) { | ||
| final int wantedSaveAmount = Integer.parseInt(in.nextLine()); | ||
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| final List<String> grid = new ArrayList<>(); | ||
| Coordinate start = null; | ||
| Coordinate end = null; | ||
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| int row = 0; | ||
| while (in.hasNextLine()) { | ||
| final String line = in.nextLine(); | ||
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| if (line.contains("S")) { | ||
| start = new Coordinate(line.indexOf('S'), row); | ||
| } | ||
| if (line.contains("E")) { | ||
| end = new Coordinate(line.indexOf('E'), row); | ||
| } | ||
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| grid.add(line); | ||
| ++row; | ||
| } | ||
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| if (start == null || end == null) { | ||
| throw new IllegalArgumentException("Start and end coordinates must be provided"); | ||
| } | ||
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| final long[][] distances = new long[grid.size()][grid.getFirst().length()]; | ||
| for (final long[] distanceRow : distances) { | ||
| Arrays.fill(distanceRow, Long.MAX_VALUE); | ||
| } | ||
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| fillFromStartToEnd(distances, grid, start, end); | ||
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| fillReachableFromEnd(distances, grid, end); | ||
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| final Map<Long, Long> savesPerAmount = getSavesPerAmount(distances, allowedCheatTime); | ||
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| long savesOverValue = 0; | ||
| for (final Map.Entry<Long, Long> entry : savesPerAmount.entrySet()) { | ||
| if (entry.getKey() >= wantedSaveAmount) { | ||
| savesOverValue += entry.getValue(); | ||
| } | ||
| } | ||
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| print(savesOverValue); | ||
| } | ||
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| private static void fillFromStartToEnd( | ||
| final long[][] distances, | ||
| final List<String> grid, | ||
| final Coordinate start, | ||
| final Coordinate end) { | ||
| final Queue<State> queue = new PriorityQueue<>(Comparator.comparingLong(State::steps)); | ||
| queue.add(new State(start, 0)); | ||
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| while (!queue.isEmpty()) { | ||
| final State state = queue.poll(); | ||
| final Coordinate coordinate = state.coordinate(); | ||
| final long steps = state.steps(); | ||
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| distances[coordinate.y()][coordinate.x()] = steps; | ||
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| if (coordinate.equals(end)) { | ||
| break; | ||
| } | ||
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| final long nextSteps = steps + 1; | ||
| visitNeighbours(distances, grid, coordinate, nextSteps, queue); | ||
| } | ||
| } | ||
|
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| private static void fillReachableFromEnd( | ||
| final long[][] distances, final List<String> grid, final Coordinate end) { | ||
| final Queue<State> queue = new PriorityQueue<>(Comparator.comparingLong(State::steps)); | ||
| queue.add(new State(end, distances[end.y()][end.x()])); | ||
|
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| while (!queue.isEmpty()) { | ||
| final State state = queue.poll(); | ||
| final Coordinate coordinate = state.coordinate(); | ||
| final long steps = state.steps(); | ||
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| distances[coordinate.y()][coordinate.x()] = steps; | ||
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| final long nextSteps = steps - 1; | ||
| visitNeighbours(distances, grid, coordinate, nextSteps, queue); | ||
| } | ||
| } | ||
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| private static void visitNeighbours( | ||
| final long[][] distances, | ||
| final List<String> grid, | ||
| final Coordinate coordinate, | ||
| final long nextSteps, | ||
| final Queue<State> queue) { | ||
| for (final Coordinate next : | ||
| Set.of( | ||
| new Coordinate(coordinate.x() - 1, coordinate.y()), | ||
| new Coordinate(coordinate.x() + 1, coordinate.y()), | ||
| new Coordinate(coordinate.x(), coordinate.y() - 1), | ||
| new Coordinate(coordinate.x(), coordinate.y() + 1))) { | ||
| if (grid.get(next.y).charAt(next.x()) != '#' && distances[next.y()][next.x()] > nextSteps) { | ||
| queue.add(new State(next, nextSteps)); | ||
| } | ||
| } | ||
| } | ||
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| private static Map<Long, Long> getSavesPerAmount( | ||
| final long[][] distances, final int allowedCheatTime) { | ||
| final Map<Long, Long> savesPerAmount = new HashMap<>(); | ||
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| for (int y1 = 1; y1 < distances.length - 1; ++y1) { | ||
| for (int x1 = 1; x1 < distances[y1].length - 1; ++x1) { | ||
| final long distance1 = distances[y1][x1]; | ||
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| if (distance1 < Long.MAX_VALUE) { | ||
| getCheatsPerStart(distances, allowedCheatTime, y1, x1, distance1, savesPerAmount); | ||
| } | ||
| } | ||
| } | ||
| return savesPerAmount; | ||
| } | ||
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| private static void getCheatsPerStart( | ||
| final long[][] distances, | ||
| final int allowedCheatTime, | ||
| final int y1, | ||
| final int x1, | ||
| final long distance1, | ||
| final Map<Long, Long> savesPerAmount) { | ||
| for (int y2 = 1; y2 < distances.length - 1; ++y2) { | ||
| for (int x2 = 1; x2 < distances[y1].length - 1; ++x2) { | ||
| final long distance2 = distances[y2][x2]; | ||
| final long cheatTime = (long) Math.abs(y1 - y2) + Math.abs(x1 - x2); | ||
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| if (distance2 < Long.MAX_VALUE && distance1 < distance2 && cheatTime <= allowedCheatTime) { | ||
| final long saveAmount = distance2 - distance1 - cheatTime; | ||
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| if (saveAmount > 0) { | ||
| savesPerAmount.put( | ||
| saveAmount, savesPerAmount.computeIfAbsent(saveAmount, key -> 0L) + 1); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| private record Coordinate(int x, int y) {} | ||
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| private record State(Coordinate coordinate, long steps) {} | ||
| } |
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