day 15

2 files changed, 100 insertions, 0 deletions

diff --git a/src/bin/2023/day15.rs b/src/bin/2023/day15.rs
new file mode 100644
index 0000000..3590938
--- /dev/null
+++ b/src/bin/2023/day15.rs
@@ -0,0 +1,98 @@
+#![allow(dead_code)]
+#![allow(unused_variables)]
+
+use advent_of_code::prelude::*;
+
+pub struct Todo;
+
+#[derive(Clone, Debug)]
+struct LensBox {
+    lenses: Vec<(String, i64)>,
+}
+
+impl LensBox {
+    fn new() -> Self {
+        Self { lenses: vec![] }
+    }
+
+    fn insert(&mut self, label: String, focal_length: i64) {
+        if let Some(idx) = self.lenses.iter().position(|(s, _)| *s == label) {
+            self.lenses[idx] = (label, focal_length);
+        } else {
+            self.lenses.push((label, focal_length));
+        }
+    }
+
+    fn remove(&mut self, label: &str) {
+        if let Some(idx) = self.lenses.iter().position(|(s, _)| *s == label) {
+            self.lenses.remove(idx);
+        }
+    }
+}
+
+fn hash(s: &str) -> usize {
+    let mut current = 0usize;
+    for c in s.bytes() {
+        current += usize::from(c);
+        current *= 17;
+        current %= 256;
+    }
+    current
+}
+
+pub fn parse(fh: File) -> Result<Vec<String>> {
+    Ok(parse::split(fh, b',').collect())
+}
+
+pub fn part1(ops: Vec<String>) -> Result<i64> {
+    Ok(ops
+        .into_iter()
+        .map(|s| hash(&s))
+        .sum::<usize>()
+        .try_into()
+        .unwrap())
+}
+
+pub fn part2(ops: Vec<String>) -> Result<i64> {
+    let mut boxes = vec![LensBox::new(); 256];
+    for op in ops {
+        if let Some(idx) = op.find('=') {
+            let label = &op[..idx];
+            let lens_box = hash(label);
+            let focal_length: i64 = op[(idx + 1)..].parse().unwrap();
+            boxes[lens_box].insert(label.to_string(), focal_length);
+        } else if op.ends_with('-') {
+            let label = &op[..(op.len() - 1)];
+            let lens_box = hash(label);
+            boxes[lens_box].remove(label);
+        }
+    }
+    Ok(boxes
+        .into_iter()
+        .enumerate()
+        .map(|(box_num, lens_box)| {
+            lens_box
+                .lenses
+                .iter()
+                .enumerate()
+                .map(|(lens_num, (_, focal_length))| {
+                    (i64::try_from(box_num).unwrap() + 1)
+                        * (i64::try_from(lens_num).unwrap() + 1)
+                        * focal_length
+                })
+                .sum::<i64>()
+        })
+        .sum())
+}
+
+#[test]
+fn test() {
+    assert_eq!(
+        part1(parse(parse::data(2023, 15).unwrap()).unwrap()).unwrap(),
+        497373
+    );
+    assert_eq!(
+        part2(parse(parse::data(2023, 15).unwrap()).unwrap()).unwrap(),
+        259356
+    );
+}
diff --git a/src/bin/2023/main.rs b/src/bin/2023/main.rs
index af0836a..31e55c5 100644
--- a/src/bin/2023/main.rs
+++ b/src/bin/2023/main.rs
@@ -25,6 +25,7 @@ mod day11;
 mod day12;
 mod day13;
 mod day14;
+mod day15;
 // NEXT MOD
 
 #[paw::main]
@@ -45,6 +46,7 @@ fn main(opt: Opt) -> Result<()> {
         12 => advent_of_code::day!(2023, opt.day, opt.puzzle, day12),
         13 => advent_of_code::day!(2023, opt.day, opt.puzzle, day13),
         14 => advent_of_code::day!(2023, opt.day, opt.puzzle, day14),
+        15 => advent_of_code::day!(2023, opt.day, opt.puzzle, day15),
         // NEXT PART
         _ => panic!("unknown day {}", opt.day),
     }