From 10245f3faa1652240eeb751e0576538be6e3fa3d Mon Sep 17 00:00:00 2001
From: Quentin Boyer <quentin+dev@familleboyer.net>
Date: Sat, 4 Jan 2025 20:38:53 +0100
Subject: [PATCH] Day 19

---
 src/bin/day19.rs | 141 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 141 insertions(+)
 create mode 100644 src/bin/day19.rs

diff --git a/src/bin/day19.rs b/src/bin/day19.rs
new file mode 100644
index 0000000..8c9386b
--- /dev/null
+++ b/src/bin/day19.rs
@@ -0,0 +1,141 @@
+use core::str;
+use std::{collections::HashMap, time::Instant};
+
+use aoc_2024::{load, print_res};
+use bstr::BString;
+use color_eyre::eyre::{bail, OptionExt};
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+pub enum Color {
+    White,
+    Blue,
+    Black,
+    Red,
+    Green,
+}
+
+impl Color {
+    fn from_b(b: u8) -> color_eyre::Result<Self> {
+        Ok(match b {
+            b'w' => Color::White,
+            b'u' => Color::Blue,
+            b'b' => Color::Black,
+            b'r' => Color::Red,
+            b'g' => Color::Green,
+            _ => bail!("Invalid color: {}", b as char),
+        })
+    }
+}
+
+type Parsed = (Vec<Vec<Color>>, Vec<Vec<Color>>);
+
+#[inline(never)]
+pub fn parsing(input: &BString) -> color_eyre::Result<Parsed> {
+    let (towels, patterns) = str::from_utf8(input)?
+        .split_once("\n\n")
+        .ok_or_eyre("Missing blank line")?;
+
+    let towels = towels
+        .split(", ")
+        .map(|towel| {
+            towel
+                .bytes()
+                .map(Color::from_b)
+                .collect::<Result<Vec<_>, _>>()
+        })
+        .collect::<Result<_, _>>()?;
+
+    let patterns = patterns
+        .lines()
+        .map(|line| {
+            line.bytes()
+                .map(Color::from_b)
+                .collect::<Result<Vec<_>, _>>()
+        })
+        .collect::<Result<_, _>>()?;
+
+    Ok((towels, patterns))
+}
+
+#[inline(never)]
+pub fn part1((towels, patterns): Parsed) {
+    let mut possible = 0;
+
+    'pattern: for pattern in patterns {
+        let mut current = vec![&*pattern];
+
+        while let Some(v) = current.pop() {
+            if v.is_empty() {
+                possible += 1;
+                continue 'pattern;
+            }
+
+            for towel in &towels {
+                if v.starts_with(towel) {
+                    current.push(&v[towel.len()..]);
+                }
+            }
+        }
+    }
+
+    print_res!("Number of possible patterns: {possible}");
+}
+
+#[inline(never)]
+pub fn part2((towels, patterns): Parsed) {
+    let mut memo = HashMap::new();
+    memo.insert(&[][..], 1);
+
+    let mut possible = 0;
+
+    fn arrangements<'a>(
+        pattern: &'a [Color],
+        towels: &[Vec<Color>],
+        memo: &mut HashMap<&'a [Color], usize>,
+    ) -> usize {
+        match memo.get(pattern) {
+            Some(&v) => v,
+            None => {
+                let value = towels
+                    .iter()
+                    .map(|towel| {
+                        if pattern.starts_with(towel) {
+                            arrangements(&pattern[towel.len()..], towels, memo)
+                        } else {
+                            0
+                        }
+                    })
+                    .sum();
+                memo.insert(pattern, value);
+                value
+            }
+        }
+    }
+
+    for pattern in &patterns {
+        possible += arrangements(pattern, &towels, &mut memo);
+    }
+
+    print_res!("Number of possible arrangements: {possible}");
+}
+
+pub fn main() -> color_eyre::Result<()> {
+    let context = load()?;
+
+    let start = Instant::now();
+    let parsed = parsing(&context.input)?;
+    let elapsed = humantime::format_duration(start.elapsed());
+
+    let start = Instant::now();
+    if context.part == 1 {
+        part1(parsed);
+    } else {
+        part2(parsed);
+    }
+    let elapsed_part = humantime::format_duration(start.elapsed());
+
+    println!("  Parsing: {elapsed}");
+    println!("  Solving: {elapsed_part}");
+
+    Ok(())
+}