Zero init > 1 init

2023/Cargo.toml

@@ -9,6 +9,7 @@ edition = "2021"
 aho-corasick = "1.1.2"
 anyhow = "1.0.75"
 clap = { version = "4.4.8", features = ["derive"] }
+linked-hash-map = "0.5.6"
 nom = "7.1.3"
 num-integer = "0.1.45"
 

2023/src/day15.rs

@@ -1,7 +1,110 @@
-pub fn part1(_input: &[u8]) -> anyhow::Result<String> {
-    anyhow::bail!("Not implemented")
+use linked_hash_map::LinkedHashMap;
+use nom::branch::alt;
+use nom::bytes::complete::tag;
+use nom::bytes::complete::take_till;
+
+use nom::combinator::map;
+use nom::multi::separated_list1;
+use nom::sequence::separated_pair;
+use nom::sequence::terminated;
+use nom::IResult;
+
+use crate::common::parse_input;
+
+fn trim(input: &[u8]) -> &[u8] {
+    let whitespace = input
+        .iter()
+        .rev()
+        .take_while(|c| c.is_ascii_whitespace())
+        .count();
+
+    &input[..(input.len() - whitespace)]
 }
 
-pub fn part2(_input: &[u8]) -> anyhow::Result<String> {
-    anyhow::bail!("Not implemented")
+fn hash(input: &[u8]) -> u8 {
+    input
+        .iter()
+        .fold(0, |cur, &c| cur.wrapping_add(c).wrapping_mul(17))
+}
+
+pub fn part1(input: &[u8]) -> anyhow::Result<String> {
+    let input = trim(input);
+
+    Ok(input
+        .split(|&c| c == b',')
+        .map(|word| u32::from(hash(word)))
+        .sum::<u32>()
+        .to_string())
+}
+
+enum Command<'a> {
+    Add(&'a [u8], u32),
+    Remove(&'a [u8]),
+}
+fn parse_commands(i: &[u8]) -> IResult<&[u8], Vec<Command>> {
+    fn is_op(c: u8) -> bool {
+        c == b'=' || c == b'-'
+    }
+
+    separated_list1(
+        tag(","),
+        alt((
+            map(
+                separated_pair(take_till(is_op), tag("="), nom::character::complete::u32),
+                |(a, b)| Command::Add(a, b),
+            ),
+            map(terminated(take_till(is_op), tag("-")), Command::Remove),
+        )),
+    )(i)
+}
+
+pub fn part2(input: &[u8]) -> anyhow::Result<String> {
+    let commands = parse_input(trim(input), parse_commands)?;
+    let mut state = LinkedHashMap::new();
+
+    for command in commands {
+        match command {
+            Command::Add(identifier, focal_len) => {
+                *state.entry(identifier).or_default() = focal_len;
+            }
+            Command::Remove(identifier) => {
+                state.remove(identifier);
+            }
+        }
+    }
+
+    let mut box_slot = [0; 256];
+    let mut total = 0;
+
+    for (&identifier, &focal_len) in &state {
+        let index = hash(identifier);
+        let box_no = u32::from(index) + 1;
+        let slot_no = &mut box_slot[index as usize];
+        *slot_no += 1;
+        total += box_no * *slot_no * focal_len;
+    }
+
+    Ok(total.to_string())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/15.txt");
+
+    #[test]
+    fn sample_hash() {
+        assert_eq!(hash(b"HASH"), 52);
+    }
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!("1320", part1(SAMPLE).unwrap());
+    }
+
+    #[test]
+    fn sample_part2() {
+        assert_eq!("145", part2(SAMPLE).unwrap());
+    }
 }

2023/src/samples/15.txt

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