Day02

2025/gareth/day02/day02.go

@@ -0,0 +1,119 @@
+package day02
+
+import (
+	"math"
+	"strconv"
+	"strings"
+)
+
+// Very messy and not my finest work but not too bad for 6am
+
+func parseInput(input string) [][2]int {
+	var ranges [][2]int
+	lines := strings.Split(strings.TrimSpace(input), ",")
+	for _, part := range lines {
+		if part == "" {
+			continue
+		}
+		ab := strings.Split(part, "-")
+		if len(ab) != 2 {
+			continue
+		}
+
+		a, _ := strconv.Atoi(ab[0])
+		b, _ := strconv.Atoi(ab[1])
+		ranges = append(ranges, [2]int{a, b})
+	}
+	return ranges
+}
+
+func divisors(n int) []int {
+	out := make([]int, 0)
+	for i := 1; i <= n; i++ {
+		if n%i == 0 {
+			out = append(out, i)
+		}
+	}
+	return out
+}
+
+func Part1(input string) int {
+	ranges := parseInput(input)
+	invalidSum := 0
+
+	for _, r := range ranges {
+		low, high := r[0], r[1]
+
+		minLen := len(strconv.Itoa(low))
+		maxLen := len(strconv.Itoa(high))
+
+		for digits := minLen; digits <= maxLen; digits++ {
+			if digits%2 != 0 {
+				continue
+			}
+
+			half := digits / 2
+			start := int(math.Pow(10, float64(half-1)))
+			end := int(math.Pow(10, float64(half)))
+
+			for first := start; first < end; first++ {
+				s := strconv.Itoa(first)
+				selected, _ := strconv.Atoi(s + s)
+
+				if selected < low {
+					continue
+				}
+				if selected > high {
+					break
+				}
+
+				invalidSum += selected
+			}
+		}
+	}
+
+	return invalidSum
+}
+
+func Part2(input string) int {
+	ranges := parseInput(input)
+	total := 0
+
+	for _, r := range ranges {
+		low, high := r[0], r[1]
+		seen := make(map[int]bool)
+
+		minLen := len(strconv.Itoa(low))
+		maxLen := len(strconv.Itoa(high))
+
+		for d := minLen; d <= maxLen; d++ {
+			for _, L := range divisors(d) {
+				k := d / L
+				if k < 2 {
+					continue
+				}
+				start := int(math.Pow(10, float64(L-1)))
+				end := int(math.Pow(10, float64(L)))
+
+				for base := start; base < end; base++ {
+					s := strings.Repeat(strconv.Itoa(base), k)
+					selected, _ := strconv.Atoi(s)
+
+					if selected < low {
+						continue
+					}
+					if selected > high {
+						break
+					}
+
+					if !seen[selected] {
+						seen[selected] = true
+						total += selected
+					}
+				}
+			}
+		}
+	}
+
+	return total
+}

2025/gareth/day02/day02_test.go

@@ -0,0 +1,17 @@
+package day02
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPart1(t *testing.T) {
+	r := Part1(`11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124`)
+	assert.Equal(t, 1227775554, r)
+}
+
+func TestPart2(t *testing.T) {
+	r := Part2(`11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124`)
+	assert.Equal(t, 4174379265, r)
+}

2025/gareth/day02/input.txt

@@ -0,0 +1 @@
+78847-119454,636-933,7143759788-7143793713,9960235-10043487,44480-68595,23468-43311,89-123,785189-1014654,3829443354-3829647366,647009-692765,2-20,30-42,120909-197026,5477469-5677783,9191900808-9191943802,1045643-1169377,46347154-46441299,2349460-2379599,719196-779497,483556-641804,265244-450847,210541-230207,195-275,75702340-75883143,58-84,2152-3237,3367-5895,1552-2029,9575-13844,6048-8966,419388311-419470147,936-1409,9292901468-9292987321

2025/gareth/main.go

@@ -1,7 +1,7 @@
 package main
 
 import (
-	"aoc/2025/day03"
+	"aoc/2025/day02"
 	"fmt"
 	"os"
 	"time"
@@ -9,9 +9,9 @@ import (
 
 func main() {
 	start := time.Now()
-	data, _ := os.ReadFile("day03/input.txt")
+	data, _ := os.ReadFile("day02/input.txt")
-	fmt.Printf("part 1: %d\n", day03.Part1(string(data)))
+	fmt.Printf("part 1: %d\n", day02.Part1(string(data)))
-	fmt.Printf("part 2: %d\n", day03.Part2(string(data)))
+	fmt.Printf("part 2: %d\n", day02.Part2(string(data)))
 	elapsed := time.Since(start)
 	fmt.Printf("Execution time: %s\n", elapsed)
 }