Solve 2024 day 1 in go

2024/go/day-01/go.mod

@@ -0,0 +1,3 @@
+module day-01
+
+go 1.23

2024/go/day-01/main.go

@@ -0,0 +1,73 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+func readInput() (leftList, rightList []int, err error) {
+	content, err := os.ReadFile("input")
+	if err != nil {
+		return
+	}
+
+	lines := strings.Split(strings.TrimSpace(string(content)), "\n")
+	for _, line := range lines {
+		parts := strings.Fields(line)
+
+		leftNum, _ := strconv.Atoi(parts[0]) // ignore error because input is always correct
+		rightNum, _ := strconv.Atoi(parts[1])
+
+		leftList = append(leftList, leftNum)
+		rightList = append(rightList, rightNum)
+	}
+
+	sort.Ints(leftList)
+	sort.Ints(rightList)
+
+	return
+}
+
+func totalDistance(leftList, rightList []int) (totalDistance int) {
+	for i := range leftList {
+		difference := leftList[i] - rightList[i]
+		if difference < 0 {
+			difference = -difference
+		}
+
+		totalDistance += difference
+	}
+
+	return
+}
+
+func similarityScore(leftList, rightList []int) (similarityScore int) {
+	rightMap := make(map[int]int)
+
+	for _, number := range rightList {
+		rightMap[number]++
+	}
+
+	for _, number := range leftList {
+		similarityScore += number * rightMap[number]
+	}
+
+	return
+}
+
+func main() {
+	leftList, rightList, err := readInput()
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	// Part one
+	fmt.Println("Total distance:", totalDistance(leftList, rightList))
+
+	// Part two
+	fmt.Println("Similarity Score:", similarityScore(leftList, rightList))
+}