Solve Day 5: Cafeteria (fresh ingredient ranges)

src/bin/05.rs

@@ -0,0 +1,110 @@
+advent_of_code::solution!(5);
+
+/// A range of fresh ingredient IDs (inclusive)
+struct FreshRange {
+    start: u64,
+    end: u64,
+}
+
+impl FreshRange {
+    fn contains(&self, id: u64) -> bool {
+        id >= self.start && id <= self.end
+    }
+}
+
+/// Parse the input into fresh ranges and available IDs
+fn parse_input(input: &str) -> (Vec<FreshRange>, Vec<u64>) {
+    // Normalize line endings and split on blank line
+    let normalized = input.replace("\r\n", "\n");
+    let mut sections = normalized.split("\n\n");
+
+    // Parse fresh ingredient ID ranges
+    let ranges_section = sections.next().unwrap_or("");
+    let ranges: Vec<FreshRange> = ranges_section
+        .lines()
+        .filter(|line| !line.trim().is_empty())
+        .map(|line| {
+            let mut parts = line.split('-');
+            let start: u64 = parts.next().unwrap().parse().unwrap();
+            let end: u64 = parts.next().unwrap().parse().unwrap();
+            FreshRange { start, end }
+        })
+        .collect();
+
+    // Parse available ingredient IDs
+    let ids_section = sections.next().unwrap_or("");
+    let ids: Vec<u64> = ids_section
+        .lines()
+        .filter(|line| !line.trim().is_empty())
+        .map(|line| line.trim().parse().unwrap())
+        .collect();
+
+    (ranges, ids)
+}
+
+/// Check if an ingredient ID is fresh (falls within any range)
+fn is_fresh(id: u64, ranges: &[FreshRange]) -> bool {
+    ranges.iter().any(|range| range.contains(id))
+}
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let (ranges, ids) = parse_input(input);
+
+    let fresh_count = ids.iter().filter(|&&id| is_fresh(id, &ranges)).count();
+
+    Some(fresh_count as u64)
+}
+
+/// Merge overlapping ranges and count total unique IDs
+fn count_unique_fresh_ids(mut ranges: Vec<FreshRange>) -> u64 {
+    if ranges.is_empty() {
+        return 0;
+    }
+
+    // Sort ranges by start
+    ranges.sort_by_key(|r| r.start);
+
+    // Merge overlapping ranges
+    let mut merged: Vec<FreshRange> = Vec::new();
+    merged.push(FreshRange {
+        start: ranges[0].start,
+        end: ranges[0].end,
+    });
+
+    for range in ranges.into_iter().skip(1) {
+        let last = merged.last_mut().unwrap();
+        // Check if ranges overlap or are adjacent
+        if range.start <= last.end + 1 {
+            // Extend the current range if needed
+            last.end = last.end.max(range.end);
+        } else {
+            // No overlap, start a new range
+            merged.push(range);
+        }
+    }
+
+    // Count total unique IDs across all merged ranges
+    merged.iter().map(|r| r.end - r.start + 1).sum()
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let (ranges, _) = parse_input(input);
+    Some(count_unique_fresh_ids(ranges))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(3));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(14));
+    }
+}