[2024] Day 22 initial solution

Author: connorslade

README.md

@@ -26,6 +26,7 @@ Thank you to [Eric Wastl](http://was.tl) for running this incredible yearly even
 - [Day 19: Linen Layout](aoc_2024/src/day_19.rs)
 - [Day 20: Race Condition](aoc_2024/src/day_20.rs)
 - [Day 21: Keypad Conundrum](aoc_2024/src/day_21.rs)
+- [Day 22: Monkey Market](aoc_2024/src/day_22.rs)
 <!-- MARKER -->
 
 ## [2023](https://adventofcode.com/2023) [![aoc_2023](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2023.yml/badge.svg)](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2023.yml)

aoc_2024/src/day_22.rs

@@ -0,0 +1,111 @@
+use std::iter::repeat;
+
+use common::{solution, Answer};
+use itertools::Itertools;
+use rayon::iter::{ParallelBridge, ParallelIterator};
+
+solution!("Monkey Market", 22);
+
+fn part_a(input: &str) -> Answer {
+    let mut sum = 0;
+
+    for num in input.lines() {
+        let mut num = num.parse::<u64>().unwrap();
+
+        for _ in 0..2000 {
+            num ^= num * 64;
+            num %= 16777216;
+
+            num ^= num / 32;
+            num %= 16777216;
+
+            num ^= num * 2048;
+            num %= 16777216;
+        }
+
+        sum += num;
+    }
+
+    sum.into()
+}
+
+fn part_b(input: &str) -> Answer {
+    let mut buyers = Vec::new();
+    let mut diffs = Vec::new();
+
+    for num in input.lines() {
+        let mut num = num.parse::<u64>().unwrap();
+        let mut seq = vec![num];
+
+        for _ in 0..2000 {
+            num ^= num * 64;
+            num %= 16777216;
+
+            num ^= num / 32;
+            num %= 16777216;
+
+            num ^= num * 2048;
+            num %= 16777216;
+
+            seq.push(num);
+        }
+
+        buyers.push(seq);
+    }
+
+    for buyer in buyers.iter() {
+        let mut diff = Vec::new();
+        for (&a, &b) in buyer.iter().tuple_windows() {
+            diff.push((b % 10) as i8 - (a % 10) as i8);
+        }
+        diffs.push(diff);
+    }
+
+    let out = repeat(-9..=9)
+        .take(4)
+        .multi_cartesian_product()
+        .par_bridge()
+        .map(|x| {
+            let (a, b, c, d) = (x[0], x[1], x[2], x[3]);
+            let mut sum = 0;
+
+            for (diff, nums) in diffs.iter().zip(buyers.iter()) {
+                let idx = diff
+                    .iter()
+                    .tuple_windows()
+                    .position(|(&ax, &bx, &cx, &dx)| ax == a && bx == b && cx == c && dx == d);
+
+                if let Some(idx) = idx {
+                    sum += nums[idx + 4] % 10;
+                }
+            }
+
+            sum
+        })
+        .max()
+        .unwrap();
+
+    out.into()
+}
+
+#[cfg(test)]
+mod test {
+    use indoc::indoc;
+
+    const CASE: &str = indoc! {"
+        1
+        10
+        100
+        2024
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(super::part_a(CASE), 37327623.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(super::part_b(CASE), 24.into());
+    }
+}

aoc_2024/src/lib.rs

@@ -21,6 +21,7 @@ mod day_18;
 mod day_19;
 mod day_20;
 mod day_21;
+mod day_22;
 // [import_marker]
 
 pub const SOLUTIONS: &[Solution] = &[
@@ -45,5 +46,6 @@ pub const SOLUTIONS: &[Solution] = &[
     day_19::SOLUTION,
     day_20::SOLUTION,
     day_21::SOLUTION,
+    day_22::SOLUTION,
     // [list_marker]
 ];