drakeerv, day 13 (#74)

Author: drakeerv

2024/13/drakeerv.v

@@ -0,0 +1,109 @@
+import os
+import arrays
+
+struct Point {
+pub mut:
+	x i64 @[required]
+	y i64 @[required]
+}
+
+fn (p Point) equals(other Point) bool {
+	return p.x == other.x && p.y == other.y
+}
+
+struct Machine {
+	a Point
+	b Point
+	t Point
+}
+
+fn parse_button(button string) Point {
+	split := button.split(', ')
+	x := i64(split[0].split('+')[1].int())
+	y := i64(split[1].split('+')[1].int())
+	return Point{
+		x: x
+		y: y
+	}
+}
+
+fn parse_target(target string) Point {
+	split := target.split(', ')
+	x := i64(split[0].split('=')[1].int())
+	y := i64(split[1].split('=')[1].int())
+	return Point{
+		x: x
+		y: y
+	}
+}
+
+fn determinant(a i64, b i64, c i64, d i64) i64 {
+	return a * d - b * c
+}
+
+fn cramers_rule(a i64, b i64, c i64, d i64, e i64, f i64) ?[2]i64 {
+	det := determinant(a, b, c, d)
+
+	if det == 0 {
+		return none
+	}
+
+	det_x := determinant(e, b, f, d)
+	det_y := determinant(a, e, c, f)
+	return [det_x / det, det_y / det]!
+}
+
+fn solve(machine Machine) ?[2]i64 {
+	result := cramers_rule(machine.a.x, machine.b.x, machine.a.y, machine.b.y, machine.t.x,
+		machine.t.y)
+
+	if result != none {
+		result_point := Point{
+			x: result[0] * machine.a.x + result[1] * machine.b.x
+			y: result[0] * machine.a.y + result[1] * machine.b.y
+		}
+		if result_point.equals(machine.t) {
+			return [result[0], result[1]]!
+		}
+	}
+	return none
+}
+
+fn main() {
+	machines := arrays.chunk(os.read_file('machines.input')!.split_into_lines().filter(it != ''),
+		3).map(fn (machine []string) Machine {
+		return Machine{
+			a: parse_button(machine[0])
+			b: parse_button(machine[1])
+			t: parse_target(machine[2])
+		}
+	})
+
+	mut tokens1 := i64(0)
+	for machine in machines {
+		result := solve(machine)
+		if result != none {
+			tokens1 += ((result[0] * 3) + result[1])
+		}
+	}
+	println('part1: ${tokens1}')
+
+	mut tokens2 := i64(0)
+	for machine in machines {
+		new_target := Point{
+			x: machine.t.x + 10000000000000
+			y: machine.t.y + 10000000000000
+		}
+		new_machine := Machine{
+			a: machine.a
+			b: machine.b
+			t: new_target
+		}
+
+		result := solve(new_machine)
+		if result != none {
+			tokens2 += ((result[0] * 3) + result[1])
+		}
+	}
+	println('part2: ${tokens2}')
+}

2024/13/machines.input

@@ -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

known/2024/13/drakeerv.out

@@ -0,0 +1,2 @@
+part1: 480
+part2: 875318608908