From 9bad216310206d12bd4413f6619e2ff8d855c2ea Mon Sep 17 00:00:00 2001
From: Jordan Doyle <jordan@doyle.la>
Date: Sun, 29 Dec 2024 01:51:27 +0700
Subject: [PATCH] Add 2024 day 22

---
 Cargo.toml |  4 ++++
 README     |  4 ++--
 2024/22.rs | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 97 insertions(+), 2 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 63b01d3..8319fad 100644
--- a/Cargo.toml
+++ a/Cargo.toml
@@ -61,5 +61,9 @@
 name = "aoc2024-21"
 path = "2024/21.rs"
 
+[[bin]]
+name = "aoc2024-22"
+path = "2024/22.rs"
+
 [lints.clippy]
 pedantic = "deny"
diff --git a/README b/README
index 6306c8e..408ff2e 100644
--- a/README
+++ a/README
@@ -35,8 +35,8 @@
 |       19 | Rust     | |       19 | Haskell  |
 |       20 | Rust     | |       20 | Haskell  |
 |       21 | Rust     | |       21 | Rust     |
-+---------------------+ |       22 | Haskell  |
-                        |       23 | Haskell  |
+|       22 | Rust     | |       22 | Haskell  |
++---------------------+ |       23 | Haskell  |
                         |       24 | Haskell  |
                         |       25 | Bash     |
                         +---------------------+
diff --git a/2024/22.rs b/2024/22.rs
new file mode 100644
index 0000000..6aca192 100644
--- /dev/null
+++ a/2024/22.rs
@@ -1,0 +1,91 @@
+#![allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
+use std::str::FromStr;
+
+fn main() -> anyhow::Result<()> {
+    let input = std::io::stdin()
+        .lines()
+        .collect::<Result<Vec<_>, _>>()?
+        .into_iter()
+        .map(|v| u32::from_str(&v))
+        .collect::<Result<Vec<_>, _>>()?;
+
+    println!("{}", part1(&input));
+    println!("{}", part2(&input));
+
+    Ok(())
+}
+
+fn part1(input: &[u32]) -> u64 {
+    let mut acc = 0;
+
+    for &i in input {
+        let mut c = i;
+
+        for _ in 0..2000 {
+            c = cipher(c);
+        }
+
+        acc += u64::from(c);
+    }
+
+    acc
+}
+
+fn part2(input: &[u32]) -> u32 {
+    const RANGE: usize = 19;
+    const OFFSET: usize = 9;
+    let mut tally =
+        vec![vec![[[0u32; RANGE]; RANGE]; RANGE].into_boxed_slice(); RANGE].into_boxed_slice();
+    let mut seen =
+        vec![vec![[[0; RANGE]; RANGE]; RANGE].into_boxed_slice(); RANGE].into_boxed_slice();
+    let mut generation = 1;
+
+    for &i in input {
+        let mut prev = cipher(i);
+        let mut a = prev;
+        let mut b = cipher(a);
+        let mut c = cipher(b);
+        let mut d = cipher(c);
+
+        for _ in 0..1998_u32 {
+            let dp = (prev % 10) as i8;
+            let da = (a % 10) as i8;
+            let db = (b % 10) as i8;
+            let dc = (c % 10) as i8;
+            let dd = (d % 10) as i8;
+
+            let delta1 = (da - dp + OFFSET as i8) as usize;
+            let delta2 = (db - da + OFFSET as i8) as usize;
+            let delta3 = (dc - db + OFFSET as i8) as usize;
+            let delta4 = (dd - dc + OFFSET as i8) as usize;
+
+            if seen[delta1][delta2][delta3][delta4] != generation {
+                seen[delta1][delta2][delta3][delta4] = generation;
+                tally[delta1][delta2][delta3][delta4] += d % 10;
+            }
+
+            prev = a;
+            a = b;
+            b = c;
+            c = d;
+            d = cipher(d);
+        }
+
+        generation += 1;
+    }
+
+    tally
+        .iter()
+        .flatten()
+        .flatten()
+        .flatten()
+        .max()
+        .copied()
+        .unwrap_or(u32::MAX)
+}
+
+fn cipher(n: u32) -> u32 {
+    let n = ((n << 6) ^ n) & 0x00FF_FFFF;
+    let n = ((n >> 5) ^ n) & 0x00FF_FFFF;
+    ((n << 11) ^ n) & 0x00FF_FFFF
+}
--
rgit 0.1.5