day 1

Author: fxnn

.gitignore

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+day?-inputs.txt

day1-example.txt

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+3   4
+4   3
+2   5
+1   3
+3   9
+3   3

day1.go

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+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"regexp"
+	"sort"
+	"strconv"
+)
+
+func convertAndAppend(list []int, strVal string) []int {
+	intVal, err := strconv.Atoi(strVal)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Couldn't convert %s to int: %s\n", strVal, err)
+		os.Exit(1)
+	}
+	return append(list, intVal)
+}
+
+func abs(x int) int {
+	if x < 0 {
+		return -x
+	}
+	return x
+}
+
+func count(list []int, val int) int {
+	count := 0
+	for _, elem := range list {
+		if elem == val {
+			count++
+		}
+	}
+	return count
+}
+
+func main() {
+	scanner := bufio.NewScanner(os.Stdin)
+	pattern := regexp.MustCompile(`^(\d+)\s+(\d+)$`)
+
+	var list1 []int
+	var list2 []int
+	for scanner.Scan() {
+		line := scanner.Text()
+		matches := pattern.FindStringSubmatch(line)
+		if len(matches) > 0 {
+			list1 = convertAndAppend(list1, matches[1])
+			list2 = convertAndAppend(list2, matches[2])
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		fmt.Fprintf(os.Stderr, "Error: %s\n", err)
+		os.Exit(1)
+	}
+
+	sort.Ints(list1)
+	sort.Ints(list2)
+	distanceSum := 0
+	for i := 0; i < len(list1); i++ {
+		distanceSum += abs(list1[i] - list2[i])
+	}
+
+	fmt.Printf("sum of distances is %d\n", distanceSum)
+
+	similarity := 0
+	for i := 0; i < len(list1); i++ {
+		similarity += list1[i] * count(list2, list1[i])
+	}
+	fmt.Printf("similarity score is %d\n", similarity)
+}

go.mod

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+module github.com/fxnn/adventofcode2024
+
+go 1.23.2