day five in the books

src/Day05.java

@@ -0,0 +1,100 @@
+package src;
+
+import java.io.FileReader;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Scanner;
+
+public class Day05 {
+    public static void main(String[] args) {
+        Instant start = Instant.now();
+        part1();
+        Instant middle = Instant.now();
+        part2();
+        Instant end = Instant.now();
+        IO.println("part 1: " + Duration.between(start, middle).toMillis() + " ms");
+        IO.println("part 2: " + Duration.between(middle, end).toMillis() + " ms");
+    }
+
+    private static void part1() {
+        try (Scanner scanner = new Scanner(new FileReader("resources/inputs/05/input"))) {
+            List<Pair<Long, Long>> ranges = new ArrayList<>();
+            List<Long> ingredients = new ArrayList<>();
+
+            while (scanner.hasNextLine()) {
+                String line = scanner.nextLine();
+                if (line.contains("-")) {
+                    String[] parts = line.split("-");
+                    long first = Long.parseLong(parts[0]);
+                    long second = Long.parseLong(parts[1]);
+                    ranges.add(new Pair<>(first, second));
+                } else if (!line.isBlank()) {
+                    ingredients.add(Long.parseLong(line));
+                }
+            }
+            int count = 0;
+            for (Long ingredient : ingredients) {
+                for (Pair<Long, Long> range : ranges) {
+                    if (ingredient >= range.head && ingredient <= range.tail) {
+                        count++;
+                        break;
+                    }
+                }
+            }
+            IO.println(count);
+        } catch (Exception e) {
+            IO.println(e.getMessage());
+        }
+    }
+
+    private static void part2() {
+        try (Scanner scanner = new Scanner(new FileReader("resources/inputs/05/input"))) {
+            List<Pair<Long, Long>> ranges = new ArrayList<>();
+
+            while (scanner.hasNextLine()) {
+                String line = scanner.nextLine();
+                if (line.contains("-")) {
+                    String[] parts = line.split("-");
+                    long first = Long.parseLong(parts[0]);
+                    long second = Long.parseLong(parts[1]);
+                    ranges.add(new Pair<>(first, second));
+                }
+            }
+            Pair<Long, Long> result = ranges.stream()
+                    .sorted((a, b) -> Long.compare(a.head, b.head))
+                    .reduce(
+                            // first is count, second is end of range covered so far
+                            new Pair<>(0L, 0L),
+                            (total, curr) -> {
+                                if (total.tail >= curr.tail) {
+                                    // this range was subsumed by a previous range
+                                    return total;
+                                }
+                                if (total.tail >= curr.head) {
+                                    // this range was partially included
+                                    return new Pair<>(total.head + (curr.tail - total.tail), curr.tail);
+                                }
+                                // this range was not previously included at all
+                                // +1 to include both endpoints
+                                return new Pair<>(total.head + (curr.tail - curr.head) + 1, curr.tail);
+                            },
+                            // merge function doesn't actually get used here but might as well write it
+                            (a, b) -> new Pair<>(a.head + b.head, Long.max(a.tail, b.tail)));
+            IO.println(result.head);
+        } catch (Exception e) {
+            IO.println(e.getMessage());
+        }
+    }
+
+    static class Pair<T, U> {
+        public final T head;
+        public final U tail;
+
+        public Pair(T first, U second) {
+            this.head = first;
+            this.tail = second;
+        }
+    }
+}