d13

res/13/example

@@ -0,0 +1,15 @@
+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

src/days/d13.rs

@@ -1,16 +1,79 @@
 use std::fs;
 
+use scan_fmt::scan_fmt;
+
 pub fn solve() {
     let path = "res/13/input";
 
     #[allow(unused)]
     let contents = fs::read_to_string(path).expect("Something went wrong reading the file");
 
-    let result: usize = 0;
+    let machines: Vec<((isize, isize), (isize, isize), (isize, isize))> = contents
+        .split("\n\n")
+        .map(|block| {
+            let (x1, y1, x2, y2, xt, yt) = scan_fmt!(
+                block,
+                "Button A: X+{}, Y+{}\nButton B: X+{}, Y+{}\nPrize: X={}, Y={}",
+                isize,
+                isize,
+                isize,
+                isize,
+                isize,
+                isize
+            )
+            .unwrap();
+            ((x1, y1), (x2, y2), (xt, yt))
+        })
+        .collect();
+
+    let result: isize = machines
+        .iter()
+        .map(|m| {
+            let ((ax, ay), (bx, by), (xt, yt)) = *m;
+            let (mut a, mut b) = (0, 0);
+            while b * bx < xt && b * by < yt {
+                b += 1;
+            }
+            while (b * bx + a * ax != xt || b * by + a * ay != yt) && b > 0 {
+                b -= 1;
+                while b * bx + a * ax < xt && b * by + a * ay < yt {
+                    a += 1;
+                }
+            }
+
+            if b * bx + a * ax == xt && b * by + a * ay == yt {
+                return b + a * 3;
+            }
+
+            return 0;
+        })
+        .sum();
 
     println!("Result 1: {}", result);
 
-    let result: usize = 0;
+    let result: isize = machines
+        .iter()
+        .map(|m| {
+            let ((ax, ay), (bx, by), (xt, yt)) = *m;
+            let xt = xt + 10000000000000;
+            let yt = yt + 10000000000000;
+
+            let b_left = by * ax - bx * ay;
+            let b_right = yt * ax - xt * ay;
+            let b = b_right / b_left;
+            if b_left * b != b_right || b < 0 {
+                return 0;
+            }
+
+            let a_left = ax;
+            let a_right = xt - b * bx;
+            let a = a_right / a_left;
+            if a_left * a != a_right || a < 0 {
+                return 0;
+            }
+            a * 3 + b
+        })
+        .sum();
 
     println!("Result 2: {}", result);
 }