From 3e9c1ee1c1900e3a67023bd1f977883810c01dda Mon Sep 17 00:00:00 2001
From: Xiretza <xiretza@xiretza.xyz>
Date: Mon, 18 Dec 2023 17:42:48 +0000
Subject: [PATCH] 2023 day15/rust: add solution

---
 2023/day15/rust/Cargo.toml  |  9 ++++++
 2023/day15/rust/src/main.rs | 56 +++++++++++++++++++++++++++++++++++++
 Cargo.lock                  |  7 +++++
 Cargo.toml                  |  1 +
 4 files changed, 73 insertions(+)
 create mode 100644 2023/day15/rust/Cargo.toml
 create mode 100644 2023/day15/rust/src/main.rs

diff --git a/2023/day15/rust/Cargo.toml b/2023/day15/rust/Cargo.toml
new file mode 100644
index 0000000..0f2e233
--- /dev/null
+++ b/2023/day15/rust/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "rust_2023_15"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+aoc = { path = "../../../common/rust" }
diff --git a/2023/day15/rust/src/main.rs b/2023/day15/rust/src/main.rs
new file mode 100644
index 0000000..3ae61b3
--- /dev/null
+++ b/2023/day15/rust/src/main.rs
@@ -0,0 +1,56 @@
+#![warn(clippy::pedantic)]
+
+use std::io::{stdin, Read};
+
+fn hash(s: &str) -> u8 {
+    s.as_bytes()
+        .iter()
+        .copied()
+        .fold(0, |acc, b| acc.wrapping_add(b).wrapping_mul(17))
+}
+
+fn main() {
+    let mut input = String::new();
+    stdin().read_to_string(&mut input).unwrap();
+    let input = input.trim();
+
+    let steps = input.split(',');
+
+    println!(
+        "{}",
+        steps.clone().map(|s| { u64::from(hash(s)) }).sum::<u64>()
+    );
+
+    let mut boxes: [Vec<(&str, usize)>; 256] = std::array::from_fn(|_| Vec::new());
+
+    for step in steps {
+        let (label, focal_length) = if let Some(label) = step.strip_suffix('-') {
+            (label, None)
+        } else {
+            let (label, focal_length) = step.split_once('=').unwrap();
+            (label, Some(focal_length.parse().unwrap()))
+        };
+
+        let b = &mut boxes[usize::from(hash(label))];
+        if let Some(existing_pos) = b.iter().position(|&(l, _fl)| l == label) {
+            if let Some(fl) = focal_length {
+                b[existing_pos].1 = fl;
+            } else {
+                b.remove(existing_pos);
+            }
+        } else if let Some(fl) = focal_length {
+            b.push((label, fl));
+        }
+    }
+
+    let focal_powers = boxes.into_iter().enumerate().flat_map(|(box_num, lenses)| {
+        lenses
+            .into_iter()
+            .enumerate()
+            .map(move |(lens_num, (_label, focal_length))| {
+                (box_num + 1) * (lens_num + 1) * focal_length
+            })
+    });
+
+    println!("{}", focal_powers.sum::<usize>());
+}
diff --git a/Cargo.lock b/Cargo.lock
index a472174..eff8c27 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -695,6 +695,13 @@ dependencies = [
  "itertools 0.12.0",
 ]
 
+[[package]]
+name = "rust_2023_15"
+version = "0.1.0"
+dependencies = [
+ "aoc",
+]
+
 [[package]]
 name = "rustversion"
 version = "1.0.14"
diff --git a/Cargo.toml b/Cargo.toml
index 7136998..1a01457 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -36,4 +36,5 @@ members = [
 	"2023/day8/rust",
 	"2023/day9/rust",
 	"2023/day11/rust",
+	"2023/day15/rust",
 ]