Updated with day 13

2024/cmd/root.go

@@ -21,6 +21,7 @@ import (
 	"cpatino.com/advent-of-code/2024/day10"
 	"cpatino.com/advent-of-code/2024/day11"
 	"cpatino.com/advent-of-code/2024/day12"
+	"cpatino.com/advent-of-code/2024/day13"
 )
 
 var days = map[int]func(string) (int, int){
@@ -36,6 +37,7 @@ var days = map[int]func(string) (int, int){
 	10: day10.Run,
 	11: day11.Run,
 	12: day12.Run,
+	13: day13.Run,
 }
 
 var rootCmd = &cobra.Command{

2024/day13/day13.go

@@ -0,0 +1,110 @@
+package day13
+
+import (
+	"bufio"
+	"fmt"
+	"math"
+	"os"
+	"regexp"
+	"strconv"
+)
+
+type Button struct {
+	X, Y int
+	cost int
+}
+
+type Machine struct {
+	A, B Button
+	X, Y int
+}
+
+func solveMachine(machine Machine) int {
+	/*
+		a * aX + b * bX = pX
+		a * aY + b * bY = pY
+	*/
+	tX := machine.X
+	tY := machine.Y
+	aX := machine.A.X
+	aY := machine.A.Y
+	bX := machine.B.X
+	bY := machine.B.Y
+
+	a := float64(tX*bY-tY*bX) / float64(aX*bY-aY*bX)
+	b := float64(tY*aX-tX*aY) / float64(aX*bY-aY*bX)
+
+	if a == math.Trunc(a) && b == math.Trunc(b) {
+		return int(a*3 + b)
+	}
+
+	return 0
+}
+
+func Part1(machines []Machine) int {
+	totalCost := 0
+	for _, machine := range machines {
+		totalCost += solveMachine(machine)
+	}
+
+	return totalCost
+}
+
+func Part2(machines []Machine) int {
+	for i := range machines {
+		machines[i].X += 10000000000000
+		machines[i].Y += 10000000000000
+	}
+
+	return Part1(machines)
+}
+
+func Run(filename string) (int, int) {
+	file, err := os.Open(filename)
+	if err != nil {
+		panic(err)
+	}
+	defer file.Close()
+
+	lines := ""
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			continue
+		}
+
+		lines += fmt.Sprintf("%s\n", line)
+	}
+
+	machines := []Machine{}
+
+	regex := regexp.MustCompile(`Button A: X\+(\d+), Y\+(\d+)\nButton B: X\+(\d+), Y\+(\d+)\nPrize: X=(\d+), Y=(\d+)`)
+	matches := regex.FindAllStringSubmatch(lines, -1)
+	for _, machine := range matches {
+		fields := make([]int, 6)
+		for i, match := range machine[1:] {
+			conv, err := strconv.Atoi(match)
+			if err != nil {
+				panic(err)
+			}
+
+			fields[i] = conv
+		}
+
+		buttonA := Button{X: fields[0], Y: fields[1], cost: 3}
+		buttonB := Button{X: fields[2], Y: fields[3], cost: 1}
+
+		machines = append(machines, Machine{A: buttonA, B: buttonB, X: fields[4], Y: fields[5]})
+	}
+
+	if err := scanner.Err(); err != nil {
+		panic(err)
+	}
+
+	part1 := Part1(machines)
+	part2 := Part2(machines)
+
+	return part1, part2
+}

2024/day13/day13_test.go

@@ -0,0 +1,44 @@
+package day13
+
+import (
+	"os"
+	"testing"
+)
+
+func TestDay13(t *testing.T) {
+	filename := "test.txt"
+	if _, err := os.Stat(filename); os.IsNotExist(err) {
+		t.Fatalf("test file does not exist: %v", filename)
+	}
+
+	part1, part2 := Run(filename)
+
+	expectedPart1 := 480
+	if part1 != expectedPart1 {
+		t.Fatalf("unexpected part1:\nwant:\t%d\ngot:\t%d", expectedPart1, part1)
+	}
+
+	expectedPart2 := 875318608908
+	if part2 != expectedPart2 {
+		t.Fatalf("unexpected part2:\nwant:\t%d\ngot:\t%d", expectedPart2, part2)
+	}
+}
+
+func TestDay13Solutions(t *testing.T) {
+	filename := "input.txt"
+	if _, err := os.Stat(filename); os.IsNotExist(err) {
+		t.Fatalf("test file does not exist: %v", filename)
+	}
+
+	part1, part2 := Run(filename)
+
+	expectedPart1 := 35997
+	if part1 != expectedPart1 {
+		t.Fatalf("unexpected part1:\nwant:\t%d\ngot:\t%d", expectedPart1, part1)
+	}
+
+	expectedPart2 := 82510994362072
+	if part2 != expectedPart2 {
+		t.Fatalf("unexpected part2:\nwant:\t%d\ngot:\t%d", expectedPart2, part2)
+	}
+}

2024/day13/test.txt

@@ -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