Implement 2023 day 15 part 1

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

@@ -1,3 +1,16 @@
+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()
@@ -8,10 +21,10 @@ fn trim(input: &[u8]) -> &[u8] {
     &input[..(input.len() - whitespace)]
 }
 
-fn hash(input: &[u8]) -> u32 {
+fn hash(input: &[u8]) -> u8 {
     input
         .iter()
-        .fold(0, |cur, &c| ((cur + u32::from(c)) * 17) % 256)
+        .fold(0, |cur, &c| cur.wrapping_add(c).wrapping_mul(17))
 }
 
 pub fn part1(input: &[u8]) -> anyhow::Result<String> {
@@ -19,13 +32,57 @@ pub fn part1(input: &[u8]) -> anyhow::Result<String> {
 
     Ok(input
         .split(|&c| c == b',')
-        .map(hash)
+        .map(|word| u32::from(hash(word)))
         .sum::<u32>()
         .to_string())
 }
 
-pub fn part2(_input: &[u8]) -> anyhow::Result<String> {
-    anyhow::bail!("Not implemented")
+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 boxes = [(); 256].map(|_| LinkedHashMap::new());
+
+    for command in &commands {
+        match command {
+            Command::Add(identifier, focal_len) => {
+                *boxes[hash(identifier) as usize]
+                    .entry(*identifier)
+                    .or_default() = *focal_len;
+            }
+            Command::Remove(identifier) => {
+                boxes[hash(identifier) as usize].remove(identifier);
+            }
+        }
+    }
+
+    let mut total = 0;
+    for (i, b) in boxes.iter().enumerate() {
+        for (slot, &focal_len) in b.values().enumerate() {
+            total += (i as u32 + 1) * (slot as u32 + 1) * focal_len;
+        }
+    }
+
+    Ok(total.to_string())
 }
 
 #[cfg(test)]
@@ -43,4 +100,9 @@ mod tests {
     fn sample_part1() {
         assert_eq!("1320", part1(SAMPLE).unwrap());
     }
+
+    #[test]
+    fn sample_part2() {
+        assert_eq!("145", part2(SAMPLE).unwrap());
+    }
 }