Day 1

day1/example.txt

@@ -0,0 +1,6 @@
+3   4
+4   3
+2   5
+1   3
+3   9
+3   3

day1/go.mod

@@ -0,0 +1,3 @@
+module stevenlr.com/aoc2024/day1
+
+go 1.22.2

day1/main.go

@@ -0,0 +1,89 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+func IntAbs(a int) int {
+	if a >= 0 {
+		return a
+	}
+	return -a
+}
+
+func main() {
+	part2(readData("data.txt"))
+}
+
+func readData(fileName string) (list1, list2 []int) {
+	fp, err := os.Open(fileName)
+	if err != nil {
+		panic(err)
+	}
+
+	scanner := bufio.NewScanner(fp)
+
+	list1 = make([]int, 0)
+	list2 = make([]int, 0)
+
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		split := strings.Split(line, "   ")
+		if len(split) != 2 {
+			continue
+		}
+
+		value1, err := strconv.Atoi(split[0])
+		if err != nil {
+			continue
+		}
+
+		value2, err := strconv.Atoi(split[1])
+		if err != nil {
+			continue
+		}
+
+		list1 = append(list1, value1)
+		list2 = append(list2, value2)
+	}
+
+	return
+}
+
+func part1(list1, list2 []int) {
+	sort.Sort(sort.IntSlice(list1))
+	sort.Sort(sort.IntSlice(list2))
+
+	dist := 0
+	for i := range list1 {
+		dist += IntAbs(list1[i] - list2[i])
+	}
+
+	fmt.Println(dist)
+}
+
+func countInstances(list []int) (counts map[int]int) {
+	counts = make(map[int]int)
+	for _, n := range list {
+		counts[n] += 1
+	}
+	return
+}
+
+func part2(list1, list2 []int) {
+	counts1 := countInstances(list1)
+	counts2 := countInstances(list2)
+
+	total := 0
+	for n, c1 := range counts1 {
+		c2, _ := counts2[n]
+		total += n * c1 * c2
+	}
+
+	fmt.Println(total)
+}