day 24 part 1

2023/data/examples/24.txt

@@ -0,0 +1,5 @@
+19, 13, 30 @ -2, 1, -2
+18, 19, 22 @ -1, -1, -2
+20, 25, 34 @ -2, -2, -4
+12, 31, 28 @ -1, -2, -1
+20, 19, 15 @ 1, -5, -3

2023/src/bin/24.rs

@@ -1,10 +1,91 @@
 advent_of_code::solution!(24);
 
-pub fn part_one(input: &str) -> Option<u32> {
-    None
+use aoc_parse::{parser, prelude::*};
+use itertools::Itertools;
+
+struct Hail {
+    id: usize,
+    x: f64,
+    y: f64,
+    z: f64,
+    dx: f64,
+    dy: f64,
+    dz: f64,
 }
 
-pub fn part_two(input: &str) -> Option<u32> {
+impl Hail {
+    fn intersect(self: &Self, other: &Hail) -> bool {
+        let bt = ((other.x - self.x) / self.dx - (other.y - self.y) / self.dy)
+            / (other.dy / self.dy - other.dx / self.dx);
+        let at = (other.x + bt * other.dx - self.x) / self.dx;
+        let ix = self.x + self.dx * at;
+        let iy = self.y + self.dy * at;
+        bt >= 0.0
+            && at >= 0.0
+            && ix >= TARGET.0
+            && ix <= TARGET.1
+            && iy >= TARGET.0
+            && iy <= TARGET.1
+    }
+}
+
+fn parse(input: &str) -> Vec<Hail> {
+    let p = parser!(lines(f64 ", " f64 ", " f64 " @ " f64 ", " f64 ", " f64));
+    p.parse(input)
+        .unwrap()
+        .iter()
+        .enumerate()
+        .map(|(index, h)| Hail {
+            id: index,
+            x: h.0,
+            y: h.1,
+            z: h.2,
+            dx: h.3,
+            dy: h.4,
+            dz: h.5,
+        })
+        .collect::<Vec<_>>()
+}
+
+#[cfg(not(test))]
+const TARGET: (f64, f64) = (200000000000000., 400000000000000.);
+
+#[cfg(test)]
+const TARGET: (f64, f64) = (7., 27.);
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let stones = parse(input);
+
+    let c = stones
+        .iter()
+        .combinations(2)
+        .filter(|st| st[0].intersect(&st[1]))
+        .count();
+    Some(c)
+}
+
+fn elim(matrix: Vec<f64>) {}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    let stones = parse(input);
+    let xymatrix = stones
+        .iter()
+        .map(|s| vec![-s.dy, s.dx, s.y, -s.x, s.y * s.dx - s.x * s.dy])
+        .collect::<Vec<_>>();
+    let lastxy = &xymatrix[xymatrix.len() - 1];
+    let xydiff = xymatrix
+        .iter()
+        .take(4)
+        .map(|r| r.iter().zip_eq(lastxy).map(|(a, b)| a - b));
+    let zmatrix = stones
+        .iter()
+        .map(|s| vec![-s.z, s.dz, s.y, -s.z, s.y * s.dz - s.z * s.dy])
+        .collect::<Vec<_>>();
+    let lastz = &zmatrix[zmatrix.len() - 1];
+    let zdiff = zmatrix
+        .iter()
+        .take(4)
+        .map(|r| r.iter().zip_eq(lastz).map(|(a, b)| a - b));
     None
 }
 
@@ -15,7 +96,7 @@ mod tests {
     #[test]
     fn test_part_one() {
         let result = part_one(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        assert_eq!(result, Some(2));
     }
 
     #[test]