2024 day 22

Author: ictrobot

crates/year2024/src/day22.rs

@@ -0,0 +1,64 @@
+use utils::prelude::*;
+
+/// Simulating a pseudorandom number generator.
+#[derive(Clone, Debug)]
+pub struct Day22 {
+    input: Vec<u32>,
+}
+
+impl Day22 {
+    pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
+        Ok(Self {
+            input: parser::number_range(0..=0xFFFFFF).parse_lines(input)?,
+        })
+    }
+
+    #[must_use]
+    pub fn part1(&self) -> u64 {
+        let mut numbers = self.input.clone();
+        for _ in 0..2000 {
+            // Inner loop over numbers allows for vectorization
+            for n in &mut numbers {
+                *n = Self::next(*n);
+            }
+        }
+        numbers.iter().map(|&n| n as u64).sum()
+    }
+
+    #[must_use]
+    pub fn part2(&self) -> u32 {
+        let mut bananas = [0; 130321]; // 19 ** 4
+        let mut seen = [0; 130321];
+        for (i, &(mut n)) in self.input.iter().enumerate() {
+            let mut index = 0;
+            let mut last_digit = n % 10;
+            for j in 0..2000 {
+                let next = Self::next(n);
+                let digit = next % 10;
+
+                index = (9 + digit - last_digit) as usize + ((index % 6859) * 19);
+                if j >= 3 && seen[index] < i + 1 {
+                    bananas[index] += next % 10;
+                    seen[index] = i + 1;
+                }
+
+                n = next;
+                last_digit = digit;
+            }
+        }
+        bananas.iter().max().copied().unwrap()
+    }
+
+    #[inline(always)]
+    fn next(mut n: u32) -> u32 {
+        n = (n ^ (n << 6)) % 0x1000000;
+        n = (n ^ (n >> 5)) % 0x1000000;
+        n = (n ^ (n << 11)) % 0x1000000;
+        n
+    }
+}
+
+examples!(Day22 -> (u64, u32) [
+    {input: "1\n10\n100\n2024", part1: 37327623},
+    {input: "1\n2\n3\n2024", part2: 23},
+]);

crates/year2024/src/lib.rs

@@ -23,4 +23,5 @@ utils::year!(2024 => year2024, ${
     19 => day19::Day19,
     20 => day20::Day20,
     21 => day21::Day21,
+    22 => day22::Day22,
 });