Day 12 - Part 2

Signed-off-by: Anthony Oteri <anthony.oteri@gmail.com>

Cargo.toml

@@ -22,6 +22,7 @@ dhat = "0.3.2"
 env_logger = "0.10.1"
 test-log = "0.2.13"
 regex = "1.10.2"
+memoize = "0.4.1"
 
 
 [profile.flamegraph]

day-12/Cargo.toml

@@ -14,6 +14,8 @@ miette = { workspace = true }
 thiserror = { workspace = true }
 dhat = { workspace = true }
 regex = { workspace = true }
+rayon = { workspace = true }
+memoize = { workspace = true }
 
 [dev-dependencies]
 divan = { workspace = true }

day-12/benches/benchmark.rs

@@ -6,10 +6,10 @@ fn main() {
 
 #[divan::bench]
 fn part1() {
-    part1::process(divan::black_box(include_str!("../test-input.txt"))).unwrap();
+    part1::process(divan::black_box(include_str!("../input.txt"))).unwrap();
 }
 
 #[divan::bench]
 fn part2() {
-    part2::process(divan::black_box(include_str!("../test-input.txt"))).unwrap();
+    part2::process(divan::black_box(include_str!("../input.txt"))).unwrap();
 }

day-12/src/part2.rs

@@ -1,8 +1,86 @@
+use nom::{
+    branch::alt,
+    bytes::complete::{tag, take_until},
+    character::complete::{self, line_ending, space1},
+    combinator::eof,
+    multi::{many1, separated_list1},
+    sequence::{self, terminated},
+    IResult,
+};
+use rayon::prelude::*;
+
 use crate::error::AocError;
 
+fn parse_input(input: &str) -> IResult<&str, &str> {
+    terminated(take_until(" "), space1)(input)
+}
+
+fn parse_limits(input: &str) -> IResult<&str, Vec<usize>> {
+    let (input, limits) = separated_list1(tag(","), complete::u32)(input)?;
+    Ok((input, limits.into_iter().map(|n| n as usize).collect()))
+}
+
+fn parser(input: &str) -> IResult<&str, Vec<(&str, Vec<usize>)>> {
+    many1(terminated(
+        sequence::tuple((parse_input, parse_limits)),
+        alt((line_ending, eof)),
+    ))(input)
+}
+
+#[memoize::memoize]
+fn count(input: String, limits: Vec<usize>) -> usize {
+    if input.is_empty() {
+        if limits.is_empty() {
+            return 1;
+        } else {
+            return 0;
+        }
+    }
+
+    if limits.is_empty() {
+        if input.contains('#') {
+            return 0;
+        } else {
+            return 1;
+        }
+    }
+    let mut n = 0;
+
+    if input.starts_with('.') || input.starts_with('?') {
+        n += count(input[1..].to_string(), limits.clone());
+    }
+    if (input.starts_with('#') || input.starts_with('?')) && limits[0] <= input.len()
+            && !input.get(..limits[0]).unwrap().contains('.') && (limits[0] == input.len() || input.chars().nth(limits[0]).unwrap() != '#') {
+        n += count(
+            input.get(limits[0] + 1..).unwrap_or_default().to_string(),
+            limits[1..].to_vec(),
+        );
+    }
+    n
+}
+
 #[tracing::instrument]
-pub fn process(input: &str) -> miette::Result<u64, AocError> {
-    Ok(0)
+pub fn process(input: &str) -> miette::Result<usize, AocError> {
+    let (_, parsed) = parser(input).unwrap();
+
+    Ok(parsed
+        .par_iter()
+        .map(|(string, limits)| {
+            let string = std::iter::repeat(string)
+                .take(5)
+                .cloned()
+                .collect::<Vec<&str>>()
+                .join("?");
+            let limits = limits
+                .iter()
+                .cycle()
+                .take(5 * limits.len())
+                .cloned()
+                .collect::<Vec<_>>();
+
+            count(string.clone(), limits)
+        })
+        .sum())
 }
 
 #[cfg(test)]
@@ -12,7 +90,7 @@ mod tests {
     #[test_log::test]
     fn test_process() -> miette::Result<()> {
         let input = include_str!("../test-input.txt");
-        assert_eq!(0, process(input)?);
+        assert_eq!(525152, process(input)?);
         Ok(())
     }
 }