Finish part-2

2025/day-05/src/part2.rs

@@ -1,11 +1,85 @@
-use miette::Result;
+use std::str::FromStr;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+struct Id(usize);
+
+impl From<usize> for Id {
+    fn from(value: usize) -> Self {
+        Self(value)
+    }
+}
+
+impl FromStr for Id {
+    type Err = String;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let num = s.trim().parse::<usize>().map_err(|e| e.to_string())?;
+        Ok(Self(num))
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+struct Range {
+    start: Id,
+    end: Id,
+}
+
+impl FromStr for Range {
+    type Err = String;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let (start_str, end_str) = s.trim().split_once('-').ok_or("`-` not found")?;
+        let start = start_str.parse::<Id>()?;
+        let end = end_str.parse::<Id>()?;
+        Ok(Self { start, end })
+    }
+}
+
+#[derive(Debug, Clone)]
+struct DB {
+    ranges: Vec<Range>,
+}
+
+impl DB {
+    fn count_range_ids(&self) -> usize {
+        let mut sorted_ranges = self.ranges.clone();
+        sorted_ranges.sort_by_key(|r| r.start.0);
+
+        let (total, start, end) =
+            sorted_ranges
+                .into_iter()
+                .fold((0, None, None), |(total, s, e), range| match (s, e) {
+                    (Some(s), Some(e)) if range.start.0 <= e + 1 => {
+                        (total, Some(s), Some(range.end.0.max(e)))
+                    }
+                    (Some(s), Some(e)) => {
+                        (total + (e - s + 1), Some(range.start.0), Some(range.end.0))
+                    }
+                    _ => (total, Some(range.start.0), Some(range.end.0)),
+                });
+
+        total + start.zip(end).map_or(0, |(s, e)| e - s + 1)
+    }
+}
+
+impl FromStr for DB {
+    type Err = String;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let (ranges_section, _) = s
+            .split_once("\n\n")
+            .ok_or("No blank line separator found")?;
+        let ranges = ranges_section
+            .lines()
+            .map(Range::from_str)
+            .collect::<Result<Vec<_>, _>>()?;
+        Ok(Self { ranges })
+    }
+}
 
 #[tracing::instrument]
 #[allow(clippy::missing_panics_doc)]
 #[allow(clippy::missing_errors_doc)]
-pub fn process(input: &str) -> Result<usize> {
-    todo!("day xx - part 2");
-    Ok(0)
+pub fn process(input: &str) -> miette::Result<usize> {
+    let db = DB::from_str(input).unwrap();
+    Ok(db.count_range_ids())
 }
 
 #[cfg(test)]
@@ -13,10 +87,20 @@ mod tests {
     use super::*;
 
     #[test]
-    fn test_process() -> Result<()> {
-        let input = "";
-        todo!("haven't built test yet");
-        let result = 0;
+    fn test_process() -> miette::Result<()> {
+        let input = "3-5
+10-14
+16-20
+12-18
+
+1
+5
+8
+11
+17
+32
+";
+        let result = 14;
         assert_eq!(process(input)?, result);
         Ok(())
     }