solve day 1 puzzle 2024

2024/day01.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"sort"
+)
+
+func part1(r io.Reader) string {
+	s := bufio.NewScanner(r)
+	var sum int
+	var left, right []int
+
+	var lft, rgh int
+	for s.Scan() {
+		fmt.Sscanf(s.Text(), "%d   %d", &lft, &rgh)
+		left, right = append(left, lft), append(right, rgh)
+	}
+
+	sort.Ints(left)
+	sort.Ints(right)
+
+	for i := range right {
+		sum += abs(left[i] - right[i])
+	}
+
+	return printi(sum)
+}
+
+func part2(r io.Reader) string {
+	s := bufio.NewScanner(r)
+	var sum int
+	var left []int
+	right := make(map[int]int)
+
+	var lft, rgh int
+	for s.Scan() {
+		fmt.Sscanf(s.Text(), "%d   %d", &lft, &rgh)
+		left = append(left, lft)
+		right[rgh]++
+	}
+
+	sort.Ints(left)
+
+	for i := range left {
+		sum += left[i] * right[left[i]]
+	}
+
+	return printi(sum)
+}
+
+func main() {
+	f, err := os.Open("day01.txt")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer f.Close()
+
+	fmt.Println(part1(f))
+	f.Seek(0, 0)
+	fmt.Println(part2(f))
+}

2024/day01_test.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestDay01(t *testing.T) {
+	input := `3   4
+4   3
+2   5
+1   3
+3   9
+3   3`
+
+	p1, p2 := strings.NewReader(input), strings.NewReader(input)
+
+	if got, expected := part1(p1), "11"; got != expected {
+		t.Errorf("day01 part 1 = %s; expected %s", got, expected)
+	}
+
+	if got, expected := part2(p2), "31"; got != expected {
+		t.Errorf("day01 part 2 = %s; expected %s", got, expected)
+	}
+}

2024/math.go

@@ -0,0 +1,9 @@
+package main
+
+func abs(i int) int {
+	r := i
+	if r < 0 {
+		r = -r
+	}
+	return r
+}

2024/print.go

@@ -0,0 +1,7 @@
+package main
+
+import "fmt"
+
+func printi(i int) string {
+	return fmt.Sprintf("%d", i)
+}

go.mod

@@ -0,0 +1,3 @@
+module adventoc
+
+go 1.19