solution: day 5

src/bin/05.rs

@@ -0,0 +1,97 @@
+use std::cmp::Ordering;
+
+use hashbrown::HashSet;
+use itertools::Itertools;
+
+#[derive(Debug)]
+struct PageUpdates {
+    raw: Vec<usize>,
+    sorted: Vec<usize>,
+}
+
+impl PageUpdates {
+    fn middle(&self) -> usize {
+        self.sorted[self.sorted.len() / 2]
+    }
+
+    fn is_sorted(&self) -> bool {
+        self.raw == self.sorted
+    }
+}
+
+fn parse_updates(input: &str) -> Vec<PageUpdates> {
+    let (page_orderings, updates) = input.split_once("\n\n").unwrap();
+
+    let mut ordering = HashSet::new();
+
+    for line in page_orderings.lines() {
+        let (a, b) = line.split_once('|').unwrap();
+        let a = a.parse().unwrap();
+        let b = b.parse().unwrap();
+        ordering.insert((a, b));
+    }
+
+    let cmp = |&a: &usize, &b: &usize| {
+        if ordering.contains(&(a, b)) {
+            Ordering::Less
+        } else if ordering.contains(&(b, a)) {
+            Ordering::Greater
+        } else {
+            Ordering::Equal
+        }
+    };
+
+    let mut page_updates = vec![];
+    for update in updates.lines() {
+        let raw = update
+            .split(',')
+            .filter_map(|x| x.parse().ok())
+            .collect_vec();
+
+        let mut sorted = raw.clone();
+        sorted.sort_by(cmp);
+
+        page_updates.push(PageUpdates { raw, sorted });
+    }
+
+    page_updates
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    parse_updates(input)
+        .iter()
+        .filter(|pu| pu.is_sorted())
+        .map(PageUpdates::middle)
+        .sum::<usize>()
+        .into()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    parse_updates(input)
+        .iter()
+        .filter(|pu| !pu.is_sorted())
+        .map(PageUpdates::middle)
+        .sum::<usize>()
+        .into()
+}
+
+aoc::solution!(5);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(
+            part_one(&aoc::template::read_file("examples", 5)),
+            Some(143)
+        );
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(
+            part_two(&aoc::template::read_file("examples", 5)),
+            Some(123)
+        );
+    }
+}