AoC 2023 Day 8 - java

pareronia · Dec 8, 2023 · 6435465 · 6435465
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diff --git a/README.md b/README.md
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 | python3 | [✓](src/main/python/AoC2023_01.py) | [✓](src/main/python/AoC2023_02.py) | [✓](src/main/python/AoC2023_03.py) | [✓](src/main/python/AoC2023_04.py) | [✓](src/main/python/AoC2023_05.py) | [✓](src/main/python/AoC2023_06.py) | [✓](src/main/python/AoC2023_07.py) | [✓](src/main/python/AoC2023_08.py) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
-| java | [✓](src/main/java/AoC2023_01.java) | [✓](src/main/java/AoC2023_02.java) | [✓](src/main/java/AoC2023_03.java) | [✓](src/main/java/AoC2023_04.java) |  | [✓](src/main/java/AoC2023_06.java) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
+| java | [✓](src/main/java/AoC2023_01.java) | [✓](src/main/java/AoC2023_02.java) | [✓](src/main/java/AoC2023_03.java) | [✓](src/main/java/AoC2023_04.java) |  | [✓](src/main/java/AoC2023_06.java) |  | [✓](src/main/java/AoC2023_08.java) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 | julia |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

diff --git a/src/main/java/AoC2023_08.java b/src/main/java/AoC2023_08.java
@@ -0,0 +1,123 @@
+import static com.github.pareronia.aoc.Utils.last;
+
+import java.math.BigInteger;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+
+import com.github.pareronia.aoc.IterTools;
+import com.github.pareronia.aoc.StringOps;
+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 AoC2023_08
+        extends SolutionBase<AoC2023_08.Map, Long, Long> {
+
+    private AoC2023_08(final boolean debug) {
+        super(debug);
+    }
+
+    public static AoC2023_08 create() {
+        return new AoC2023_08(false);
+    }
+
+    public static AoC2023_08 createDebug() {
+        return new AoC2023_08(true);
+    }
+
+    @Override
+    protected Map parseInput(final List<String> inputs) {
+        return Map.fromInput(inputs);
+    }
+
+    @Override
+    public Long solvePart1(final Map map) {
+        return map.steps("AAA");
+    }
+
+    @Override
+    public Long solvePart2(final Map map) {
+        return map.forks().keySet().stream()
+            .filter(key -> last(key) == 'A')
+            .map(map::steps)
+            .map(BigInteger::valueOf)
+            .reduce((a, b) -> a.multiply(b).divide(a.gcd(b)))
+            .get().longValue();
+    }
+
+    @Override
+    @Samples({
+        @Sample(method = "part1", input = TEST1, expected = "2"),
+        @Sample(method = "part1", input = TEST2, expected = "6"),
+        @Sample(method = "part2", input = TEST3, expected = "6"),
+    })
+    public void samples() {
+    }
+
+    public static void main(final String[] args) throws Exception {
+        AoC2023_08.create().run();
+    }
+
+    record Map(List<Character> instructions, java.util.Map<String, Fork> forks) {
+        private record Fork(String left, String right) {}
+
+        public static Map fromInput(final List<String> lines) {
+            final List<List<String>> blocks = StringOps.toBlocks(lines);
+            final List<Character> instructions
+                    = Utils.asCharacterStream(blocks.get(0).get(0)).toList();
+            final java.util.Map<String, Fork> forks = new HashMap<>();
+            for (final String line : blocks.get(1)) {
+                final String[] splits = line.split(" = ");
+                forks.put(
+                    splits[0],
+                    new Fork(splits[1].substring(1, 4), splits[1].substring(6, 9)));
+            }
+            return new Map(instructions, forks);
+        }
+
+        public long steps(String key) {
+            final Iterator<Character> inss = IterTools.cycle(this.instructions);
+            Fork fork = this.forks.get(key);
+            long ans = 0;
+            while (last(key) != 'Z') {
+                key = inss.next() == 'L' ? fork.left : fork.right;
+                fork = this.forks.get(key);
+                ans++;
+            }
+            return ans;
+        }
+    }
+
+    private static final String TEST1 = """
+            RL
+            
+            AAA = (BBB, CCC)
+            BBB = (DDD, EEE)
+            CCC = (ZZZ, GGG)
+            DDD = (DDD, DDD)
+            EEE = (EEE, EEE)
+            GGG = (GGG, GGG)
+            ZZZ = (ZZZ, ZZZ)
+            """;
+    private static final String TEST2 = """
+            LLR
+            
+            AAA = (BBB, BBB)
+            BBB = (AAA, ZZZ)
+            ZZZ = (ZZZ, ZZZ)
+            """;
+    private static final String TEST3 = """
+            LR
+            
+            11A = (11B, XXX)
+            11B = (XXX, 11Z)
+            11Z = (11B, XXX)
+            22A = (22B, XXX)
+            22B = (22C, 22C)
+            22C = (22Z, 22Z)
+            22Z = (22B, 22B)
+            XXX = (XXX, XXX)
+            """;
+}