solution: day 15

data/examples/15.txt

@@ -0,0 +1 @@
+rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7

src/bin/15.rs

@@ -0,0 +1,68 @@
+fn hash(s: &str) -> usize {
+    let mut total = 0;
+    for c in s.chars().map(|x| x as usize) {
+        total += c;
+        total *= 17;
+        total %= 256;
+    }
+    total
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    Some(input.lines().flat_map(|x| x.split(',')).map(hash).sum())
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    let mut map = vec![Vec::<(&str, usize)>::new(); 256];
+
+    for instruction in input.lines().flat_map(|x| x.split(',')) {
+        let (label, n) = instruction.split_once(|x| x == '-' || x == '=').unwrap();
+        let hash = hash(label);
+        let indexed_map = map.get_mut(hash).unwrap();
+
+        if instruction.contains('-') {
+            if let Some((i, _)) = indexed_map.iter().enumerate().find(|(_, &x)| x.0 == label) {
+                indexed_map.remove(i);
+            }
+        } else {
+            let nbr = n.parse().unwrap();
+            if let Some((i, _)) = indexed_map.iter().enumerate().find(|(_, &x)| x.0 == label) {
+                indexed_map[i] = (label, nbr);
+            } else {
+                indexed_map.push((label, nbr))
+            }
+        }
+    }
+
+    Some(
+        map.into_iter()
+            .enumerate()
+            .flat_map(|(i, x)| {
+                x.into_iter()
+                    .enumerate()
+                    .map(move |(j, y)| (i + 1) * (j + 1) * y.1)
+            })
+            .sum(),
+    )
+}
+
+aoc::solution!(15);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(
+            part_one(&aoc::template::read_file("examples", 15)),
+            Some(1320)
+        );
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(
+            part_two(&aoc::template::read_file("examples", 15)),
+            Some(145)
+        );
+    }
+}