day13 solution 1

1 files changed, 95 insertions, 0 deletions

diff --git a/src/bin/day13.rs b/src/bin/day13.rs
new file mode 100644
index 0000000..965d7c0
--- /dev/null
+++ b/src/bin/day13.rs
@@ -0,0 +1,95 @@
+use regex::Regex;
+
+static DAY: u8 = 13;
+
+fn main() {
+    let input = advent::read_file(DAY);
+    println!("{DAY}a: {}", win_tokens(input.trim_end()));
+    println!("{DAY}b: {}", 0);
+}
+
+struct Machine {
+    button_a: (u32, u32),
+    button_b: (u32, u32),
+    prize: (u32, u32),
+}
+
+impl Machine {
+    fn new(input: &str) -> Machine {
+        let re_a = Regex::new(r"Button A: X\+(\d+), Y\+(\d+)").unwrap();
+        let re_b = Regex::new(r"Button B: X\+(\d+), Y\+(\d+)").unwrap();
+        let re_p = Regex::new(r"Prize: X=(\d+), Y=(\d+)").unwrap();
+
+        let lines = input.split("\n").collect::<Vec<_>>();
+        let button_a = lines[0];
+        let button_b = lines[1];
+        let prizes = lines[2];
+
+        let captures_a = re_a.captures(button_a).unwrap();
+        let captures_b = re_b.captures(button_b).unwrap();
+        let captures_p = re_p.captures(prizes).unwrap();
+
+        let a_x = captures_a.get(1).unwrap().as_str().parse::<u32>().unwrap();
+        let a_y = captures_a.get(2).unwrap().as_str().parse::<u32>().unwrap();
+        let b_x = captures_b.get(1).unwrap().as_str().parse::<u32>().unwrap();
+        let b_y = captures_b.get(2).unwrap().as_str().parse::<u32>().unwrap();
+        let p_x = captures_p.get(1).unwrap().as_str().parse::<u32>().unwrap();
+        let p_y = captures_p.get(2).unwrap().as_str().parse::<u32>().unwrap();
+
+        Machine {
+            button_a: (a_x, a_y),
+            button_b: (b_x, b_y),
+            prize: (p_x, p_y),
+        }
+    }
+
+    fn lowest_prize(&self) -> Option<u32> {
+        let mut best_prize = None;
+        for a in 0 ..= 100 {
+            for b in 0 ..= 100 {
+                if (a * self.button_a.0) + (b * self.button_b.0) != self.prize.0 {
+                    continue;
+                }
+                if (a * self.button_a.1) + (b * self.button_b.1) != self.prize.1 {
+                    continue;
+                }
+                let prize = 3 * a + b;
+                best_prize = Some(best_prize.unwrap_or(u32::MAX).min(prize));
+            }
+        }
+        best_prize
+    }
+}
+
+fn win_tokens(input: &str) -> u32 {
+    input.split("\n\n")
+         .map(Machine::new)
+         .map(|machine| machine.lowest_prize().unwrap_or(0))
+         .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input =
+"Button A: X+94, Y+34
+Button B: X+22, Y+67
+Prize: X=8400, Y=5400
+
+Button A: X+26, Y+66
+Button B: X+67, Y+21
+Prize: X=12748, Y=12176
+
+Button A: X+17, Y+86
+Button B: X+84, Y+37
+Prize: X=7870, Y=6450
+
+Button A: X+69, Y+23
+Button B: X+27, Y+71
+Prize: X=18641, Y=10279";
+        assert_eq!(win_tokens(&input), 480);
+    }
+}