day 13 pt2

src/bin/13.rs

@@ -10,10 +10,10 @@ struct Point<T> {
 }
 
 #[derive(Debug, Copy, Clone)]
-struct Machine {
-    a_button: Point<u32>,
-    b_button: Point<u32>,
-    prize: Point<u32>
+struct Machine<T> {
+    a_button: Point<T>,
+    b_button: Point<T>,
+    prize: Point<T>
 }
 
 pub fn part_one(input: &str) -> Option<u32> {
@@ -25,35 +25,80 @@ pub fn part_one(input: &str) -> Option<u32> {
         assert!(lines.len() >= 3);
 
         let c_a = r_button.captures(lines[0]).unwrap();
-        let a_button = Point { x: c_a[2].parse::<u32>().unwrap(), y: c_a[3].parse::<u32>().unwrap() };
+        let a_button = Point { x: c_a[2].parse::<usize>().unwrap(), y: c_a[3].parse::<usize>().unwrap() };
 
         let c_b = r_button.captures(lines[1]).unwrap();
-        let b_button = Point { x: c_b[2].parse::<u32>().unwrap(), y: c_b[3].parse::<u32>().unwrap() };
+        let b_button = Point { x: c_b[2].parse::<usize>().unwrap(), y: c_b[3].parse::<usize>().unwrap() };
 
         let c_p = r_prize.captures(lines[2]).unwrap();
-        let prize = Point { x: c_p[1].parse::<u32>().unwrap(), y: c_p[2].parse::<u32>().unwrap() };
+        let prize = Point { x: c_p[1].parse::<usize>().unwrap(), y: c_p[2].parse::<usize>().unwrap() };
 
         Machine { a_button, b_button, prize }
     }).collect_vec();
 
     // println!("MACHINES {:?}", machines);
     // BRUTE FORCE SOLUTION
-    let total_tokens: u32 = machines.iter().map(|machine| {
+    let total_tokens: usize = machines.iter().map(|machine| {
         let matches = find_matches(*machine).collect_vec();
         let min = matches.iter().map(|(x, y)| 3 * x + y).min().unwrap_or(0);
         // println!("MATCHES {:?}", matches);
         min
     }).sum();
 
-    Some(total_tokens)
+    Some(total_tokens as u32)
 }
 
-pub fn part_two(_input: &str) -> Option<u32> {
-    None
+pub fn part_two(input: &str) -> Option<u64> {
+    const OFFSET: isize = 10000000000000;
+    let r_button = Regex::new(r"Button (A|B): X\+(\d+), Y\+(\d+)").unwrap();
+    let r_prize = Regex::new(r"Prize: X=(\d+), Y=(\d+)").unwrap();
+
+    let machines = input.lines().chunks(4).into_iter().map(|chunk| {
+        let lines = chunk.collect_vec();
+        assert!(lines.len() >= 3);
+
+        let c_a = r_button.captures(lines[0]).unwrap();
+        let a_button = Point { x: c_a[2].parse::<isize>().unwrap(), y: c_a[3].parse::<isize>().unwrap() };
+
+        let c_b = r_button.captures(lines[1]).unwrap();
+        let b_button = Point { x: c_b[2].parse::<isize>().unwrap(), y: c_b[3].parse::<isize>().unwrap() };
+
+        let c_p = r_prize.captures(lines[2]).unwrap();
+        let prize = Point { x: c_p[1].parse::<isize>().unwrap() + OFFSET, y: c_p[2].parse::<isize>().unwrap() + OFFSET };
+
+        Machine { a_button, b_button, prize }
+    }).collect_vec();
+
+    println!("PROCESSING {} MACHINES", machines.len());
+    let wins = machines.iter().filter_map(|Machine { a_button, b_button, prize }| {
+
+        let denom = (a_button.x * b_button.y) - (a_button.y * b_button.x );
+        let a_numer = (prize.x * b_button.y) - (prize.y * b_button.x);
+        let b_numer = (prize.y * a_button.x) - (prize.x * a_button.y);
+
+        if a_numer % denom != 0 || b_numer % denom != 0 {
+            print!("❌");
+            return None;
+        }
+
+        let a_presses = a_numer / denom;
+        let b_presses = b_numer / denom;
+
+        print!("✔️ ");
+        Some(3 * a_presses + b_presses)
+        // println!("MATCHES {:?}", matches);
+    }).collect_vec();
+
+    println!();
+    println!("WON {} PRIZES!", wins.len());
+
+    let total_tokens: isize = wins.into_iter().sum();
+    println!("COST {} TOKENS!", total_tokens);
+    Some(total_tokens as u64)
 }
 
 // TODO figure out how to reference-ify this
-fn find_matches(machine: Machine) -> impl Iterator<Item=(u32, u32)> {
+fn find_matches(machine: Machine<usize>) -> impl Iterator<Item=(usize, usize)> {
     (0..=100).flat_map(move |a_presses| {
         (0..=100).filter_map(move |b_presses| {
             let pos_x = machine.a_button.x * a_presses + machine.b_button.x * b_presses;
@@ -81,6 +126,6 @@ mod tests {
     #[test]
     fn test_part_two() {
         let result = part_two(&advent_of_code::template::read_file("examples", DAY));
-        assert_eq!(result, None);
+        assert_eq!(result, Some(3440247820));
     }
 }