AoC 2024 Day 2 - java

README.md

@@ -9,7 +9,7 @@
 | | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |
 | ---| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
 | python3 | [✓](src/main/python/AoC2024_01.py) | [✓](src/main/python/AoC2024_02.py) | [✓](src/main/python/AoC2024_03.py) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
-| java | [✓](src/main/java/AoC2024_01.java) |  | [✓](src/main/java/AoC2024_03.java) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
+| java | [✓](src/main/java/AoC2024_01.java) | [✓](src/main/java/AoC2024_02.java) | [✓](src/main/java/AoC2024_03.java) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
 | rust | [✓](src/main/rust/AoC2024_01/src/main.rs) | [✓](src/main/rust/AoC2024_02/src/main.rs) | [✓](src/main/rust/AoC2024_03/src/main.rs) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
 <!-- @END:ImplementationsTable:2024@ -->
 

src/main/java/AoC2024_02.java

@@ -0,0 +1,84 @@
+import static com.github.pareronia.aoc.IntegerSequence.Range.range;
+import static com.github.pareronia.aoc.IterTools.windows;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import com.github.pareronia.aoc.Utils;
+import com.github.pareronia.aoc.solution.Sample;
+import com.github.pareronia.aoc.solution.Samples;
+import com.github.pareronia.aoc.solution.SolutionBase;
+
+public final class AoC2024_02
+        extends SolutionBase<List<List<Integer>>, Integer, Integer> {
+
+    private AoC2024_02(final boolean debug) {
+        super(debug);
+    }
+
+    public static AoC2024_02 create() {
+        return new AoC2024_02(false);
+    }
+
+    public static AoC2024_02 createDebug() {
+        return new AoC2024_02(true);
+    }
+
+    @Override
+    protected List<List<Integer>> parseInput(final List<String> inputs) {
+        return inputs.stream()
+            .map(line -> Arrays.stream(line.split(" "))
+                    .map(Integer::parseInt)
+                    .toList())
+            .toList();
+    }
+
+    private boolean safe(final List<Integer> levels) {
+        final List<Integer> diffs = Utils.stream(windows(levels))
+            .map(w -> w.second() - w.first())
+            .toList();
+        return diffs.stream().allMatch(diff -> 1 <= diff && diff <= 3)
+            || diffs.stream().allMatch(diff -> -1 >= diff && diff >= -3);
+    }
+
+    @Override
+    public Integer solvePart1(final List<List<Integer>> reports) {
+        return (int) reports.stream().filter(this::safe).count();
+    }
+
+    @Override
+    public Integer solvePart2(final List<List<Integer>> reports) {
+        return (int) reports.stream()
+            .filter(report ->
+                range(report.size()).intStream()
+                    .mapToObj(i -> {
+                        final List<Integer> tmp = new ArrayList<>(report);
+                        tmp.remove(i);
+                        return tmp;
+                    })
+                    .anyMatch(this::safe)
+            ).count();
+    }
+
+    @Override
+    @Samples({
+        @Sample(method = "part1", input = TEST, expected = "2"),
+        @Sample(method = "part2", input = TEST, expected = "4"),
+    })
+    public void samples() {
+    }
+
+    public static void main(final String[] args) throws Exception {
+        AoC2024_02.create().run();
+    }
+
+    private static final String TEST = """
+            7 6 4 2 1
+            1 2 7 8 9
+            9 7 6 2 1
+            1 3 2 4 5
+            8 6 4 4 1
+            1 3 6 7 9
+            """;
+}

src/main/java/com/github/pareronia/aoc/IterTools.java

@@ -155,6 +155,25 @@ public static <T> Iterator<T> cycle(final Iterable<T> iterable) {
         return cycle(iterable.iterator());
     }
 
+    public static <T> Iterator<WindowPair<T>> windows(final List<T> list) {
+        return new Iterator<>() {
+            int i = 0;
+
+            @Override
+            public boolean hasNext() {
+                return i < list.size() - 1;
+            }
+
+            @Override
+            public WindowPair<T> next() {
+                final WindowPair<T> next
+                        = new WindowPair<>(list.get(i), list.get(i + 1));
+                i++;
+                return next;
+            }
+        };
+    }
+
     private static final class Heap {
 
         public static void accept(final int[] a, final Consumer<int[]> consumer) {
@@ -193,5 +212,7 @@ private static void swap(final int[] a, final int i, final int j) {
 
     public record ZippedPair<T>(T first, T second) {}
 
+    public record WindowPair<T>(T first, T second) {}
+
     public record Enumerated<T>(int index, T value) {}
 }

src/test/java/com/github/pareronia/aoc/IterToolsTestCase.java

@@ -10,6 +10,7 @@
 
 import org.junit.jupiter.api.Test;
 
+import com.github.pareronia.aoc.IterTools.WindowPair;
 import com.github.pareronia.aoc.IterTools.ZippedPair;
 
 public class IterToolsTestCase {
@@ -78,4 +79,14 @@ public void cycle() {
             assertThat(ccycle.next()).isEqualTo('c');
         }
    }
+
+    @Test
+    public void windows() {
+        final Iterator<WindowPair<Integer>> windows
+                = IterTools.windows(List.of(1, 2, 3, 4));
+        assertThat(windows.next()).isEqualTo(new WindowPair<>(1, 2));
+        assertThat(windows.next()).isEqualTo(new WindowPair<>(2, 3));
+        assertThat(windows.next()).isEqualTo(new WindowPair<>(3, 4));
+        assertThat(windows.hasNext()).isFalse();
+    }
 }