solution: day 13

src/bin/13.rs

@@ -0,0 +1,79 @@
+use regex::Regex;
+
+fn parse_input(input: &str) -> Vec<[(isize, isize); 3]> {
+    let r = Regex::new(r".*X(?:=|\+)(\d*), Y(?:=|\+)(\d*)").unwrap();
+
+    let mut parsed = Vec::new();
+
+    for machine in input.split("\n\n") {
+        let mut p = [(0, 0); 3];
+        for (idx, line) in machine.lines().enumerate() {
+            let c = r.captures(line).unwrap();
+            let x: isize = c.get(1).unwrap().as_str().parse().unwrap();
+            let y: isize = c.get(2).unwrap().as_str().parse().unwrap();
+
+            p[idx] = (x, y);
+        }
+        parsed.push(p)
+    }
+
+    parsed
+}
+
+fn solve(m: ((isize, isize), (isize, isize)), v: (isize, isize)) -> Option<isize> {
+    let det = m.0 .0 * m.1 .1 - m.0 .1 * m.1 .0;
+
+    if det == 0 {
+        return None;
+    }
+
+    let x = (v.0 * m.1 .1 - m.0 .1 * v.1) as f64 / det as f64;
+    let y = (m.0 .0 * v.1 - v.0 * m.1 .0) as f64 / det as f64;
+
+    if x.trunc() != x || y.trunc() != y {
+        return None;
+    }
+
+    Some(x as isize * 3 + y as isize)
+}
+
+pub fn part_one(input: &str) -> Option<isize> {
+    parse_input(input)
+        .into_iter()
+        .filter_map(|[(a1, b1), (a2, b2), t]| solve(((a1, a2), (b1, b2)), t))
+        .sum::<isize>()
+        .into()
+}
+
+pub fn part_two(input: &str) -> Option<isize> {
+    let prize_add = 10_000_000_000_000;
+
+    parse_input(input)
+        .into_iter()
+        .filter_map(|[(a0, b0), (a1, b1), (t0, t1)]| {
+            solve(((a0, a1), (b0, b1)), (t0 + prize_add, t1 + prize_add))
+        })
+        .sum::<isize>()
+        .into()
+}
+
+aoc::solution!(13);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(
+            part_one(&aoc::template::read_file("examples", 13)),
+            Some(480)
+        );
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(
+            part_two(&aoc::template::read_file("examples", 13)),
+            Some(875318608908)
+        );
+    }
+}