day 1

day1/main.go

@@ -0,0 +1,97 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func readLines(filename string) []string {
+	raw, err := os.ReadFile(filename)
+	if err != nil {
+		panic(err)
+	}
+	return strings.Split(string(raw), "\n")
+}
+
+func parseLine(line string) (int, error) {
+	var c int
+	switch {
+	case strings.HasPrefix(line, "R"):
+		c = 1
+	case strings.HasPrefix(line, "L"):
+		c = -1
+	default:
+		return 0, fmt.Errorf("invalid line")
+	}
+	x, err := strconv.Atoi(line[1:])
+	if err != nil {
+		return c, err
+	}
+	if x <= 0 {
+		return x, fmt.Errorf("non-positive value")
+	}
+	return c * x, nil
+}
+
+func countZeros(lines []string) int {
+	count := 0
+	current := 50
+	max := 100
+	for _, line := range lines {
+		if line == "" {
+			continue
+		}
+		x, err := parseLine(line)
+		if err != nil {
+			panic(err)
+		}
+		current = (current + x) % max
+		if current == 0 {
+			count++
+		}
+	}
+	return count
+}
+
+func countClicks(lines []string) int {
+	count := 0
+	current := 50
+	max := 100
+	for _, line := range lines {
+		if line == "" {
+			continue
+		}
+		x, err := parseLine(line)
+		if err != nil {
+			panic(err)
+		}
+		for {
+			if x > 0 {
+				x--
+				current++
+				if current == 0 || current == max {
+					count++
+					current = 0
+				}
+			} else if x < 0 {
+				x++
+				current--
+				if current == 0 || current == -max {
+					count++
+					current = 0
+				}
+			} else {
+				break
+			}
+		}
+	}
+	return count
+}
+
+func main() {
+	lines := readLines("part1.txt")
+	println(countZeros(lines))
+	println(countClicks(lines))
+}

day1/part0.txt

@@ -0,0 +1,10 @@
+L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82

go.mod

@@ -0,0 +1,3 @@
+module ballstads.name/aoc2025
+
+go 1.25.5