Refactor input parsing

Author: gdejong

cmd/day1/main.go

@@ -1,100 +1,85 @@
 package main
 
 import (
-	"bufio"
 	"fmt"
+	"github.com/gdejong/advent-of-code-2024/internal/input"
 	"github.com/gdejong/advent-of-code-2024/internal/must"
-	"io"
-	"os"
 	"slices"
 )
 
 func main() {
-	f := must.NoError(os.Open("cmd/day1/real_input.txt"))
+	lines := input.Content("cmd/day1/real_input.txt")
 
-	part1answer := part1(f)
-	fmt.Println(part1answer)
+	fmt.Println(part1(lines))
 
-	// Reset the file so we can it again for part 2
-	must.NoError(f.Seek(0, io.SeekStart))
-
-	part2answer := part2(f)
-	fmt.Println(part2answer)
+	fmt.Println(part2(lines))
 }
 
-func part2(f *os.File) int {
-	s := bufio.NewScanner(f)
-
+func part1(lines []string) int {
 	var leftList []int
 	var rightList []int
 
-	for s.Scan() {
-		line := s.Text()
-
+	for _, line := range lines {
 		var leftNumber int
 		var rightNumber int
 		must.NoError(fmt.Sscanf(line, "%d %d", &leftNumber, &rightNumber))
 		leftList = append(leftList, leftNumber)
 		rightList = append(rightList, rightNumber)
 	}
 
-	counterMap := make(map[int]int)
+	slices.Sort(leftList)
+	slices.Sort(rightList)
 
-	for _, value := range rightList {
-		if _, ok := counterMap[value]; ok {
-			counterMap[value]++
-		} else {
-			counterMap[value] = 1
-		}
+	if len(leftList) != len(rightList) {
+		panic("expected same length")
 	}
 
-	similarityScore := 0
-	for _, value := range leftList {
-		counterMapValue, ok := counterMap[value]
-		if !ok {
-			continue
+	distanceSum := 0
+	for i := 0; i < len(leftList); i++ {
+		distance := leftList[i] - rightList[i]
+
+		// Take the absolute value
+		if distance < 0 {
+			distance = distance * -1
 		}
 
-		similarityScore += value * counterMapValue
+		distanceSum += distance
 	}
 
-	return similarityScore
+	return distanceSum
 }
 
-func part1(f *os.File) int {
-	s := bufio.NewScanner(f)
-
+func part2(lines []string) int {
 	var leftList []int
 	var rightList []int
 
-	for s.Scan() {
-		line := s.Text()
-
+	for _, line := range lines {
 		var leftNumber int
 		var rightNumber int
 		must.NoError(fmt.Sscanf(line, "%d %d", &leftNumber, &rightNumber))
 		leftList = append(leftList, leftNumber)
 		rightList = append(rightList, rightNumber)
 	}
 
-	slices.Sort(leftList)
-	slices.Sort(rightList)
+	counterMap := make(map[int]int)
 
-	if len(leftList) != len(rightList) {
-		panic("expected same length")
+	for _, value := range rightList {
+		if _, ok := counterMap[value]; ok {
+			counterMap[value]++
+		} else {
+			counterMap[value] = 1
+		}
 	}
 
-	distanceSum := 0
-	for i := 0; i < len(leftList); i++ {
-		distance := leftList[i] - rightList[i]
-
-		// Take the absolute value
-		if distance < 0 {
-			distance = distance * -1
+	similarityScore := 0
+	for _, value := range leftList {
+		counterMapValue, ok := counterMap[value]
+		if !ok {
+			continue
 		}
 
-		distanceSum += distance
+		similarityScore += value * counterMapValue
 	}
 
-	return distanceSum
+	return similarityScore
 }

cmd/day1/main_test.go

@@ -1,25 +1,24 @@
 package main
 
 import (
-	"github.com/gdejong/advent-of-code-2024/internal/must"
-	"os"
+	"github.com/gdejong/advent-of-code-2024/internal/input"
 	"testing"
 )
 
 func TestPart1(t *testing.T) {
-	f := must.NoError(os.Open("test_input.txt"))
+	lines := input.Content("test_input.txt")
 
-	answer := part1(f)
+	answer := part1(lines)
 
 	if answer != 11 {
 		t.Errorf("wrong answer, got: %d", answer)
 	}
 }
 
 func TestPart2(t *testing.T) {
-	f := must.NoError(os.Open("test_input.txt"))
+	lines := input.Content("test_input.txt")
 
-	answer := part2(f)
+	answer := part2(lines)
 
 	if answer != 31 {
 		t.Errorf("wrong answer, got: %d", answer)

cmd/day2/main.go

@@ -1,35 +1,24 @@
 package main
 
 import (
-	"bufio"
 	"fmt"
 	"github.com/gdejong/advent-of-code-2024/internal/input"
 	"github.com/gdejong/advent-of-code-2024/internal/math"
-	"github.com/gdejong/advent-of-code-2024/internal/must"
 	"github.com/gdejong/advent-of-code-2024/internal/slices"
-	"io"
-	"os"
 	"strings"
 )
 
 func main() {
-	f := must.NoError(os.Open("cmd/day2/real_input.txt"))
+	lines := input.Content("cmd/day2/real_input.txt")
 
-	fmt.Println(part1(f))
+	fmt.Println(part1(lines))
 
-	// Reset the file so we can it again for part 2
-	must.NoError(f.Seek(0, io.SeekStart))
-
-	fmt.Println(part2(f))
+	fmt.Println(part2(lines))
 }
 
-func part1(f *os.File) int {
-	s := bufio.NewScanner(f)
-
+func part1(lines []string) int {
 	safeCounter := 0
-	for s.Scan() {
-		line := s.Text()
-
+	for _, line := range lines {
 		report := input.ToIntegers(strings.Fields(line))
 
 		if isSafeReport(report) {
@@ -40,20 +29,16 @@ func part1(f *os.File) int {
 	return safeCounter
 }
 
-func part2(f *os.File) int {
-	s := bufio.NewScanner(f)
-
+func part2(lines []string) int {
 	safeCounter := 0
-	for s.Scan() {
-		line := s.Text()
-
+	for _, line := range lines {
 		report := input.ToIntegers(strings.Fields(line))
 
 		// Create all possible options by continually removing one level
 		var reportsToCheck [][]int
 		reportsToCheck = append(reportsToCheck, report)
 		for index := range len(report) {
-			reportsToCheck = append(reportsToCheck, remove(report, index))
+			reportsToCheck = append(reportsToCheck, slices.CopyAndRemoveIndex(report, index))
 		}
 
 		for _, r := range reportsToCheck {
@@ -67,12 +52,6 @@ func part2(f *os.File) int {
 	return safeCounter
 }
 
-func remove(slice []int, s int) []int {
-	s2 := make([]int, len(slice))
-	copy(s2, slice)
-	return append(s2[:s], s2[s+1:]...)
-}
-
 func isSafeReport(levels []int) bool {
 	// Calculate the differences
 	diffs := make([]int, len(levels)-1)

cmd/day2/main_test.go

@@ -1,25 +1,24 @@
 package main
 
 import (
-	"github.com/gdejong/advent-of-code-2024/internal/must"
-	"os"
+	"github.com/gdejong/advent-of-code-2024/internal/input"
 	"testing"
 )
 
 func TestPart1(t *testing.T) {
-	f := must.NoError(os.Open("test_input.txt"))
+	lines := input.Content("test_input.txt")
 
-	answer := part1(f)
+	answer := part1(lines)
 
 	if answer != 2 {
 		t.Errorf("wrong answer, got: %d", answer)
 	}
 }
 
 func TestPart2(t *testing.T) {
-	f := must.NoError(os.Open("test_input.txt"))
+	lines := input.Content("test_input.txt")
 
-	answer := part2(f)
+	answer := part2(lines)
 
 	if answer != 4 {
 		t.Errorf("wrong answer, got: %d", answer)

internal/input/input.go

@@ -1,10 +1,28 @@
 package input
 
 import (
+	"bufio"
 	"github.com/gdejong/advent-of-code-2024/internal/must"
+	"os"
 	"strconv"
 )
 
+func Content(file string) []string {
+	f, err := os.Open(file)
+	if err != nil {
+		panic(err)
+	}
+	defer f.Close()
+	s := bufio.NewScanner(f)
+
+	lines := make([]string, 0)
+	for s.Scan() {
+		lines = append(lines, s.Text())
+	}
+
+	return lines
+}
+
 func ToIntegers(input []string) []int {
 	integers := make([]int, len(input))
 

internal/math/math.go

@@ -1,5 +1,6 @@
 package math
 
+// Abs returns the absolute value of value.
 func Abs(value int) int {
 	if value < 0 {
 		value = value * -1

internal/slices/slices.go

@@ -9,3 +9,11 @@ func All[T any](ts []T, pred func(T) bool) bool {
 	}
 	return true
 }
+
+// CopyAndRemoveIndex returns a new slice with the given i element removed.
+func CopyAndRemoveIndex(slice []int, i int) []int {
+	newSlice := make([]int, len(slice))
+	copy(newSlice, slice) // make a copy so we do not alter the original slice
+
+	return append(newSlice[:i], newSlice[i+1:]...)
+}