day14

aoc_2024/src/day14.rs

@@ -0,0 +1,128 @@
+use std::sync::OnceLock;
+
+use aoc_runner_derive::{aoc, aoc_generator};
+
+use nom::{
+    bytes::complete::tag,
+    character::complete::{i64 as parse_i64, newline, space1},
+    error::Error,
+    multi::separated_list0,
+    sequence::{preceded, separated_pair},
+};
+
+type Input = Vec<((i64, i64), (i64, i64))>;
+
+#[aoc_generator(day14)]
+fn parse(input: &str) -> Input {
+    separated_list0(
+        newline::<&str, Error<&str>>,
+        separated_pair(
+            preceded(tag("p="), separated_pair(parse_i64, tag(","), parse_i64)),
+            space1,
+            preceded(tag("v="), separated_pair(parse_i64, tag(","), parse_i64)),
+        ),
+    )(input)
+    .unwrap()
+    .1
+}
+
+#[aoc(day14, part1)]
+fn part1(input: &Input) -> i64 {
+    #[cfg(test)]
+    let (w, h) = (7, 11);
+    #[cfg(not(test))]
+    let (w, h) = (101, 103);
+
+    let mut quadrants = [0, 0, 0, 0];
+
+    input.iter().copied().for_each(|(p, v)| {
+        let (px, py) = (p.0, p.1);
+        let (vx, vy) = (v.0 + w, v.1 + h);
+        let (ex, ey) = ((px + vx * 100) % w, (py + vy * 100) % h);
+        if ex < w / 2 && ey < h / 2 {
+            quadrants[0] += 1;
+        } else if ex > (w - 1) / 2 && ey < h / 2 {
+            quadrants[1] += 1;
+        } else if ex < w / 2 && ey > (h - 1) / 2 {
+            quadrants[2] += 1;
+        } else if ex > (w - 1) / 2 && ey > (h - 1) / 2 {
+            quadrants[3] += 1;
+        }
+    });
+
+    quadrants.iter().product()
+}
+
+#[aoc(day14, part2)]
+fn part2(input: &Input) -> usize {
+    let (w, h) = (101, 103);
+
+    let mut input = input.clone();
+
+    let mut iter = 0;
+
+    loop {
+        iter += 1;
+
+        let mut total = (0f64, 0f64);
+        input = input
+            .into_iter()
+            .map(|((px, py), (vx, vy))| {
+                let (px, py) = ((px + vx + w) % w, (py + vy + h) % h);
+                total.0 += px as f64;
+                total.1 += py as f64;
+                ((px, py), (vx, vy))
+            })
+            .collect();
+        let mean = (total.0 / input.len() as f64, total.1 / input.len() as f64);
+        let variance = input
+            .iter()
+            .map(|((px, py), _)| {
+                let dx = *px as f64 - mean.0;
+                let dy = *py as f64 - mean.1;
+                dx * dx + dy * dy
+            })
+            .sum::<f64>()
+            / input.len() as f64;
+
+        if variance < 1000.0 {
+            break;
+        }
+    }
+
+    iter
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(
+            part1(&parse(
+                "p=0,4 v=3,-3
+p=6,3 v=-1,-3
+p=10,3 v=-1,2
+p=2,0 v=2,-1
+p=0,0 v=1,3
+p=3,0 v=-2,-2
+p=7,6 v=-1,-3
+p=3,0 v=-1,-2
+p=9,3 v=2,3
+p=7,3 v=-1,2
+p=2,4 v=2,-3
+p=9,5 v=-3,-3"
+            )),
+            12
+        );
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(
+            part2(&parse(include_str!("../input/2024/day14.txt").trim_end())),
+            6398
+        );
+    }
+}

aoc_2024/src/lib.rs

@@ -3,6 +3,7 @@ mod day10;
 mod day11;
 mod day12;
 mod day13;
+mod day14;
 mod day2;
 mod day3;
 mod day4;