2021 day 25

Author: jeffrpowell

src/main/java/com/jeffrpowell/adventofcode/Launcher.java

@@ -9,7 +9,7 @@
 
 public class Launcher
 {
-	public static final Solution<?> DAY = new Day23();
+	public static final Solution<?> DAY = new Day25();
 
     public static void main(String[] args) {
 		InputStream puzzleInputStream = Thread.currentThread().getContextClassLoader().getResourceAsStream(getInputFileName(DAY));

src/main/java/com/jeffrpowell/adventofcode/aoc2021/Day25.java

@@ -0,0 +1,142 @@
+package com.jeffrpowell.adventofcode.aoc2021;
+
+import java.awt.geom.Point2D;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Stream;
+
+import com.jeffrpowell.adventofcode.Point2DUtils;
+import com.jeffrpowell.adventofcode.inputparser.InputParser;
+import com.jeffrpowell.adventofcode.inputparser.InputParserFactory;
+
+public class Day25 extends Solution2021<List<String>> {
+    Map<Point2D, Occupant> grid;
+    Set<Point2D> unlockedPts;
+    boolean changed = true;
+    int maxX; 
+    int maxY;
+
+    @Override
+    public int getDay() {
+        return 25;
+    }
+
+    @Override
+    public InputParser<List<String>> getInputParser() {
+        return InputParserFactory.getTokenSVParser("");
+    }
+
+    @Override
+    protected String part1(List<List<String>> input) {
+        grid = new HashMap<>();
+        unlockedPts = new HashSet<>();
+        maxX = input.get(0).size() - 1;
+        maxY = input.size() - 1;
+        for (int y = 0; y < input.size(); y++) {
+            for (int x = 0; x < input.get(0).size(); x++) {
+                String value = input.get(y).get(x);
+                Occupant o = Occupant.fromString(value);
+                Point2D pt = new Point2D.Double(x, y);
+                grid.put(pt, o);
+                if (o == Occupant.EMPTY) {
+                    unlockedPts.add(pt);
+                }
+            }
+        }
+        long i = 0;
+        while(changed) {
+            i++;
+            changed = false;
+            stepEast();
+            stepSouth();
+        }
+        return Long.toString(i);
+    }
+
+    private void stepEast() {
+        Map<Point2D, Point2D> moves = new HashMap<>();
+        for (Point2D dest : unlockedPts) {
+            Point2D src = getWesternNeighbor(dest);
+            if (grid.get(src) == Occupant.EAST) {
+                moves.put(src, dest);
+            }
+        }
+        moves.entrySet().stream().forEach(entry -> {
+            grid.put(entry.getKey(), Occupant.EMPTY);
+            grid.put(entry.getValue(), Occupant.EAST);
+        });
+        unlockedPts.removeAll(moves.values());
+        unlockedPts.addAll(moves.keySet());
+        if (!moves.isEmpty()) {
+            changed = true;
+        }
+    }
+
+    private void stepSouth() {
+        Map<Point2D, Point2D> moves = new HashMap<>();
+        for (Point2D dest : unlockedPts) {
+            Point2D src = getNorthernNeighbor(dest);
+            if (grid.get(src) == Occupant.SOUTH) {
+                moves.put(src, dest);
+            }
+        }
+        moves.entrySet().stream().forEach(entry -> {
+            grid.put(entry.getKey(), Occupant.EMPTY);
+            grid.put(entry.getValue(), Occupant.SOUTH);
+        });
+        unlockedPts.removeAll(moves.values());
+        unlockedPts.addAll(moves.keySet());
+        if (!moves.isEmpty()) {
+            changed = true;
+        }
+    }
+
+    @Override
+    protected String part2(List<List<String>> input) {
+        // TODO Auto-generated method stub
+        return null;
+    }
+    
+    enum Occupant {
+        EMPTY, EAST, SOUTH;
+
+        public static Occupant fromString(String value) {
+            if (value.equals("v")) {
+                return Occupant.SOUTH;
+            }
+            else if (value.equals(">")) {
+                return Occupant.EAST;
+            }
+            else {
+                return Occupant.EMPTY;
+            }
+        }
+    }
+
+    private Stream<Point2D> getNorthernNeighbors(Set<Point2D> pts) {
+        return pts.stream().map(this::getNorthernNeighbor);
+    }
+
+    private Point2D getNorthernNeighbor(Point2D pt) {
+        Point2D p = Point2DUtils.applyVectorToPt(new Point2D.Double(0, -1), pt);
+        if (p.getY() < 0) {
+            p.setLocation(p.getX(), maxY);
+        }
+        return p;
+    }
+
+    private Stream<Point2D> getWesternNeighbors(Set<Point2D> pts) {
+        return pts.stream().map(this::getWesternNeighbor);
+    }
+
+    private Point2D getWesternNeighbor(Point2D pt) {
+        Point2D p = Point2DUtils.applyVectorToPt(new Point2D.Double(-1, 0), pt);
+        if (p.getX() < 0) {
+            p.setLocation(maxX, p.getY());
+        }
+        return p;
+    }
+}