22th day

Author: majcn

data/examples/22-1.txt

@@ -0,0 +1,4 @@
+1
+10
+100
+2024

data/examples/22-2.txt

@@ -0,0 +1,4 @@
+1
+2
+3
+2024

src/bin/22.rs

@@ -0,0 +1,88 @@
+advent_of_code::solution!(22);
+
+use advent_of_code::maneatingape::hash::*;
+use advent_of_code::maneatingape::parse::*;
+
+fn parse_data(input: &str) -> Vec<u32> {
+    input.lines().map(|line| line.unsigned()).collect()
+}
+
+const MASK_8_BITS: u32 = (1 << 8) - 1;
+const MASK_24_BITS: u32 = (1 << 24) - 1;
+
+#[allow(clippy::let_and_return)]
+fn next_price(secret_number: u32) -> u32 {
+    let secret_number = secret_number << 6 & MASK_24_BITS ^ secret_number;
+    let secret_number = secret_number >> 5 ^ secret_number;
+    let secret_number = secret_number << 11 & MASK_24_BITS ^ secret_number;
+
+    secret_number
+}
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let data = parse_data(input);
+
+    let result = data
+        .into_iter()
+        .map(|secret_number| {
+            (0..2000).fold(secret_number, |secret_number, _| next_price(secret_number)) as u64
+        })
+        .sum();
+
+    Some(result)
+}
+
+pub fn part_two(input: &str) -> Option<u32> {
+    let data = parse_data(input);
+
+    let mut prices = FastMap::new();
+
+    for (i, secret_number) in data.into_iter().enumerate() {
+        let mut secret_number = secret_number;
+        let mut prev_cost = secret_number % 10;
+
+        let mut four_changes = 0;
+
+        for n in 0..2000 {
+            secret_number = next_price(secret_number);
+            let cost = secret_number % 10;
+
+            four_changes <<= 8;
+            four_changes |= cost.wrapping_sub(prev_cost) & MASK_8_BITS;
+
+            if n >= 4 {
+                prices.entry((i, four_changes)).or_insert(cost);
+            }
+
+            prev_cost = cost;
+        }
+    }
+
+    let mut best_results = FastMap::with_capacity(prices.len());
+    for ((_, four_changes), cost) in prices.into_iter() {
+        *best_results.entry(four_changes).or_insert(0) += cost;
+    }
+
+    let result = best_results.into_values().max().unwrap();
+
+    Some(result)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let input = advent_of_code::template::read_file_part("examples", DAY, 1);
+        let result = part_one(&input);
+        assert_eq!(result, Some(37327623));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let input = advent_of_code::template::read_file_part("examples", DAY, 2);
+        let result = part_two(&input);
+        assert_eq!(result, Some(23));
+    }
+}