Day 15 and Day 16

Author: Alextopher

Cargo.lock

@@ -45,8 +45,8 @@ members = [
     "y23/d12-hot-springs",
     "y23/d13-point-of-incidence",
     "y23/d14-parabolic-reflector-dish",
-    "y23/d15",
-    "y23/d16",
+    "y23/d15-lens-library",
+    "y23/d16-the-floor-will-be-lava",
     "y23/d17",
     "y23/d18",
     "y23/d19",

Cargo.toml

@@ -48,7 +48,7 @@ Graph Cycle, Shoelace Theorem
 
 ### Day 11 - Cosmic Expansion
 
-A very sparse matrix
+A very sparse graph
 
 ### Day 12 - Hot Springs
 
@@ -60,12 +60,16 @@ Dynamic Programming
 
 ### Day 14 - Parabolic Reflector Dish
 
-[Falling rocks](../y22/README.md#day-14), cycle detection
+[Falling rocks](../y22/README.md#day-14), cycle detection, hoping hashes don't collide
 
-### Day 15
+### Day 15 - Lens Library
+
+Homemade `HashMap`
 
 ### Day 16
 
+BFS
+
 ### Day 17
 
 ### Day 18

y23/README.md

@@ -8,4 +8,4 @@ edition = "2021"
 [dependencies]
 aoc = { path = "../../aoc" }
 itertools = "0.12.0"
-nohash-hasher = "0.2.0"
+nohash-hasher = "0.2.0"

y23/d14-parabolic-reflector-dish/Cargo.toml

@@ -0,0 +1,93 @@
+use std::collections::VecDeque;
+
+use aoc::input_str;
+
+fn hash(s: &str) -> u8 {
+    s.bytes().fold(0, |acc, b| (acc + b) * 17)
+}
+
+fn part1(input: &str) -> u32 {
+    input
+        .split(',')
+        .map(|s| s.trim())
+        .map(hash)
+        .map(|h| h as u32)
+        .sum()
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+struct Value<'a> {
+    label: &'a str,
+    value: u8,
+}
+
+struct Hashmap<'a> {
+    buckets: Vec<VecDeque<Value<'a>>>,
+}
+
+impl<'a> Hashmap<'a> {
+    fn new() -> Self {
+        Self {
+            buckets: vec![VecDeque::new(); 256],
+        }
+    }
+
+    fn get_bucket(&mut self, label: &'a str) -> &mut VecDeque<Value<'a>> {
+        &mut self.buckets[hash(label) as usize]
+    }
+
+    fn insert(&mut self, label: &'a str, value: u8) {
+        let bucket = self.get_bucket(label);
+        if let Some(v) = bucket.iter_mut().find(|v| v.label == label) {
+            v.value = value;
+        } else {
+            bucket.push_back(Value { label, value });
+        }
+    }
+
+    fn remove(&mut self, label: &'a str) {
+        let bucket = self.get_bucket(label);
+        if let Some(pos) = bucket.iter().position(|v| v.label == label) {
+            bucket.remove(pos);
+        }
+    }
+
+    fn score(&self) -> u32 {
+        self.buckets
+            .iter()
+            .zip(1..)
+            .flat_map(|(b, i)| {
+                b.iter()
+                    .zip(1..)
+                    .map(move |(v, j)| (v.value as u32) * i * j)
+            })
+            .sum::<u32>()
+    }
+}
+
+fn part2(input: &str) -> u32 {
+    let instructions = input.split(',').map(|s| s.trim());
+
+    // Instruction is either
+    // - "label=value" (set label)
+    // or
+    // - "label-" (remove label)
+    let mut hashmap = Hashmap::new();
+    for instruction in instructions {
+        if let Some(label) = &instruction.strip_suffix('-') {
+            hashmap.remove(label);
+        } else {
+            let mut parts = instruction.split('=');
+            let label = parts.next().unwrap();
+            let value = parts.next().unwrap().parse::<u8>().unwrap();
+            hashmap.insert(label, value);
+        }
+    }
+    hashmap.score()
+}
+
+fn main() {
+    let input = input_str!(2023, 15);
+    println!("Part 1: {}", part1(input));
+    println!("Part 2: {}", part2(input));
+}

y23/d15/Cargo.toml renamed to y23/d15-lens-library/Cargo.toml

@@ -7,3 +7,4 @@ edition = "2021"
 
 [dependencies]
 aoc = { path = "../../aoc" }
+rayon = "1.8.0"