Solve day 12 part 2

Cargo.lock

@@ -2,6 +2,18 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "ahash"
+version = "0.8.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "91429305e9f0a25f6205c5b8e0d2db09e0708a7a6df0f42212bb56c32c8ac97a"
+dependencies = [
+ "cfg-if",
+ "once_cell",
+ "version_check",
+ "zerocopy",
+]
+
 [[package]]
 name = "aho-corasick"
 version = "1.1.2"
@@ -11,6 +23,12 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "allocator-api2"
+version = "0.2.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0942ffc6dcaadf03badf6e6a2d0228460359d5e34b57ccdc720b7382dfbd5ec5"
+
 [[package]]
 name = "anyhow"
 version = "1.0.75"
@@ -22,6 +40,7 @@ name = "aoc2023"
 version = "0.0.0"
 dependencies = [
  "anyhow",
+ "cached",
  "indicatif",
  "itertools",
  "rayon",
@@ -36,6 +55,39 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
 
+[[package]]
+name = "cached"
+version = "0.46.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c7c8c50262271cdf5abc979a5f76515c234e764fa025d1ba4862c0f0bcda0e95"
+dependencies = [
+ "ahash",
+ "cached_proc_macro",
+ "cached_proc_macro_types",
+ "hashbrown",
+ "instant",
+ "once_cell",
+ "thiserror",
+]
+
+[[package]]
+name = "cached_proc_macro"
+version = "0.18.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c878c71c2821aa2058722038a59a67583a4240524687c6028571c9b395ded61f"
+dependencies = [
+ "darling",
+ "proc-macro2",
+ "quote",
+ "syn 1.0.109",
+]
+
+[[package]]
+name = "cached_proc_macro_types"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3a4f925191b4367301851c6d99b09890311d74b0d43f274c0b34c86d308a3663"
+
 [[package]]
 name = "cfg-if"
 version = "1.0.0"
@@ -88,6 +140,41 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "darling"
+version = "0.14.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7b750cb3417fd1b327431a470f388520309479ab0bf5e323505daf0290cd3850"
+dependencies = [
+ "darling_core",
+ "darling_macro",
+]
+
+[[package]]
+name = "darling_core"
+version = "0.14.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "109c1ca6e6b7f82cc233a97004ea8ed7ca123a9af07a8230878fcfda9b158bf0"
+dependencies = [
+ "fnv",
+ "ident_case",
+ "proc-macro2",
+ "quote",
+ "strsim",
+ "syn 1.0.109",
+]
+
+[[package]]
+name = "darling_macro"
+version = "0.14.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a4aab4dbc9f7611d8b55048a3a16d2d010c2c8334e46304b40ac1cc14bf3b48e"
+dependencies = [
+ "darling_core",
+ "quote",
+ "syn 1.0.109",
+]
+
 [[package]]
 name = "either"
 version = "1.9.0"
@@ -100,6 +187,28 @@ version = "0.3.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a357d28ed41a50f9c765dbfe56cbc04a64e53e5fc58ba79fbc34c10ef3df831f"
 
+[[package]]
+name = "fnv"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
+
+[[package]]
+name = "hashbrown"
+version = "0.14.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "290f1a1d9242c78d09ce40a5e87e7554ee637af1351968159f4952f028f75604"
+dependencies = [
+ "ahash",
+ "allocator-api2",
+]
+
+[[package]]
+name = "ident_case"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b9e0384b61958566e926dc50660321d12159025e767c18e043daf26b70104c39"
+
 [[package]]
 name = "indicatif"
 version = "0.17.7"
@@ -171,6 +280,12 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "830b246a0e5f20af87141b25c173cd1b609bd7779a4617d6ec582abaf90870f3"
 
+[[package]]
+name = "once_cell"
+version = "1.19.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3fdb12b2476b595f9358c5161aa467c2438859caa136dec86c26fdd2efe17b92"
+
 [[package]]
 name = "portable-atomic"
 version = "1.5.1"
@@ -273,7 +388,7 @@ checksum = "43576ca501357b9b071ac53cdc7da8ef0cbd9493d8df094cd821777ea6e894d3"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn",
+ "syn 2.0.39",
 ]
 
 [[package]]
@@ -287,6 +402,23 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "strsim"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
+
+[[package]]
+name = "syn"
+version = "1.0.109"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72b64191b275b66ffe2469e8af2c1cfe3bafa67b529ead792a6d0160888b4237"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
 [[package]]
 name = "syn"
 version = "2.0.39"
@@ -298,6 +430,26 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "thiserror"
+version = "1.0.51"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f11c217e1416d6f036b870f14e0413d480dbf28edbee1f877abaf0206af43bb7"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "1.0.51"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "01742297787513b79cf8e29d1056ede1313e2420b7b3b15d0a768b4921f549df"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.39",
+]
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.12"
@@ -310,6 +462,12 @@ version = "0.1.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e51733f11c9c4f72aa0c160008246859e340b00807569a0da0e7a1079b27ba85"
 
+[[package]]
+name = "version_check"
+version = "0.9.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
+
 [[package]]
 name = "windows-sys"
 version = "0.45.0"
@@ -375,3 +533,23 @@ name = "windows_x86_64_msvc"
 version = "0.42.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9aec5da331524158c6d1a4ac0ab1541149c0b9505fde06423b02f5ef0106b9f0"
+
+[[package]]
+name = "zerocopy"
+version = "0.7.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1c4061bedbb353041c12f413700357bec76df2c7e2ca8e4df8bac24c6bf68e3d"
+dependencies = [
+ "zerocopy-derive",
+]
+
+[[package]]
+name = "zerocopy-derive"
+version = "0.7.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b3c129550b3e6de3fd0ba67ba5c81818f9805e58b8d7fee80a3a59d2c9fc601a"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.39",
+]

Cargo.toml

@@ -5,6 +5,7 @@ edition = "2021"
 
 [dependencies]
 anyhow = "1.0.75"
+cached = "0.46.1"
 indicatif = { version = "0.17.7", features = ["rayon"] }
 itertools = "0.12.0"
 rayon = "1.8.0"

src/bin/12.rs

@@ -1,12 +1,14 @@
 use aoc2023::*;
-use std::collections::VecDeque;
+use cached::proc_macro::cached;
+use itertools::Itertools;
+use std::{collections::VecDeque, fmt::Debug, iter};
 
 const INPUT: &str = include_str!("../../input/12");
 
 fn main() {
     assert_example!(part1, "12-test", 21);
     println!("Part 1: {}", part1(INPUT));
-    assert_example!(part2, "12-test", 0);
+    assert_example!(part2, "12-test", 525152);
     println!("Part 2: {}", part2(INPUT));
 }
 
@@ -14,15 +16,20 @@ fn part1(input: &str) -> usize {
     input
         .lines()
         .map(Row::parse)
-        .map(Row::possible_arrangements)
+        .map(possible_arrangements)
         .sum()
 }
 
 fn part2(input: &str) -> usize {
-    0
+    input
+        .lines()
+        .map(Row::parse)
+        .map(Row::unfold)
+        .map(possible_arrangements)
+        .sum()
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
 struct Row {
     springs: VecDeque<Spring>,
     groups: VecDeque<usize>,
@@ -36,11 +43,22 @@ impl Row {
         Self { springs, groups }
     }
 
-    fn possible_arrangements(mut self) -> usize {
+    fn unfold(self) -> Self {
+        let springs = iter::repeat(self.springs).take(5);
+        let springs = Itertools::intersperse(springs, [Spring::Unknown].into())
+            .flatten()
+            .collect();
+        let groups = iter::repeat(self.groups).take(5).flatten().collect();
+        Self { springs, groups }
+    }
+}
+
+#[cached]
+fn possible_arrangements(mut row: Row) -> usize {
     // Pop all operational springs on the front and then get the first different one.
     let first = loop {
-            match self.springs.pop_front() {
+        match row.springs.pop_front() {
-                None => return if self.groups.is_empty() { 1 } else { 0 },
+            None => return if row.groups.is_empty() { 1 } else { 0 },
             Some(Spring::Operational) => continue,
             Some(Spring::Broken) => break InterestingSpring::Broken,
             Some(Spring::Unknown) => break InterestingSpring::Unknown,
@@ -50,7 +68,7 @@ impl Row {
     match first {
         InterestingSpring::Broken => {
             // A broken spring requires a run that matches the group.
-                let Some(mut group) = self.groups.pop_front() else {
+            let Some(mut group) = row.groups.pop_front() else {
                 // There was a broken spring but no group
                 return 0;
             };
@@ -60,27 +78,25 @@ impl Row {
 
             // Pop all required springs or return if impossible.
             loop {
-                    match self.springs.pop_front() {
+                match row.springs.pop_front() {
                     None if group > 0 => return 0,
-                        None if group == 0 => break,
+                    None => break,
                     Some(Spring::Broken | Spring::Unknown) if group > 0 => group -= 1,
-                        Some(Spring::Broken) if group == 0 => return 0,
+                    Some(Spring::Broken) => return 0,
                     Some(Spring::Operational) if group > 0 => return 0,
                     Some(Spring::Operational | Spring::Unknown) => break,
-                        other => panic!("group detection weird case {other:?}, group={group}"),
                 }
             }
 
-                self.possible_arrangements()
+            possible_arrangements(row)
         }
         InterestingSpring::Unknown => {
             // We don't know what kind of spring is here, recursively try both options.
-                let mut a = self.clone();
+            let mut a = row.clone();
-                let mut b = self;
+            let mut b = row;
             a.springs.push_front(Spring::Broken);
             b.springs.push_front(Spring::Operational);
-                a.possible_arrangements() + b.possible_arrangements()
+            possible_arrangements(a) + possible_arrangements(b)
-            }
         }
     }
 }
@@ -91,7 +107,7 @@ enum InterestingSpring {
     Unknown,
 }
 
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
 enum Spring {
     Broken,
     Unknown,