day22

aoc_2024/src/day22.rs

@@ -0,0 +1,88 @@
+use aoc_runner_derive::{aoc, aoc_generator};
+
+type Input = Vec<usize>;
+
+#[aoc_generator(day22)]
+fn parse(input: &str) -> Input {
+    input.lines().map(|n| n.parse().unwrap()).collect()
+}
+
+#[inline(always)]
+fn next_number(number: usize) -> usize {
+    let step1 = (number ^ (number << 6)) % (1 << 24);
+    let step2 = (step1 ^ (step1 >> 5)) % (1 << 24);
+    (step2 ^ step2 << 11) % (1 << 24)
+}
+
+#[inline(always)]
+fn step_2000(number: usize) -> usize {
+    let mut number = number;
+    for _ in 0..2000 {
+        number = next_number(number);
+    }
+    number
+}
+
+#[aoc(day22, part1)]
+fn part1(input: &Input) -> usize {
+    input.iter().map(|n| step_2000(*n)).sum()
+}
+
+#[aoc(day22, part2)]
+fn part2(input: &Input) -> usize {
+    let mut total = Box::new([[[[0; 19]; 19]; 19]; 19]);
+    let mut max_total = 0;
+    let mut last_monkey = Box::new([[[[0; 19]; 19]; 19]; 19]);
+    for (monkey, secret) in input.iter().enumerate() {
+        let mut one = *secret;
+        let mut two = next_number(one);
+        let mut three = next_number(two);
+        let mut four = next_number(three);
+        for _ in 0..2000 - 3 {
+            let next = next_number(four);
+
+            let idx_1 = (two % 10) - (one % 10) + 9;
+            let idx_2 = (three % 10) - (two % 10) + 9;
+            let idx_3 = (four % 10) - (three % 10) + 9;
+            let idx_4 = (next % 10) - (four % 10) + 9;
+
+            if last_monkey[idx_1][idx_2][idx_3][idx_4] <= monkey {
+                last_monkey[idx_1][idx_2][idx_3][idx_4] = monkey + 1;
+                total[idx_1][idx_2][idx_3][idx_4] += next % 10;
+                max_total = max_total.max(total[idx_1][idx_2][idx_3][idx_4]);
+            }
+
+            one = two;
+            two = three;
+            three = four;
+            four = next;
+        }
+    }
+    max_total
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse("1")), 8685429);
+        assert_eq!(part1(&parse("10")), 4700978);
+        assert_eq!(part1(&parse("100")), 15273692);
+        assert_eq!(part1(&parse("2024")), 8667524);
+    }
+
+    //     #[test]
+    //     fn part2_example() {
+    //         assert_eq!(
+    //             part2(&parse(
+    //                 "1
+    // 10
+    // 100
+    // 2024"
+    //             )),
+    //             23
+    //         );
+    //     }
+}

aoc_2024/src/lib.rs

@@ -1,3 +1,4 @@
+mod day22;
 mod day21;
 mod day1;
 mod day10;