[2024] Solution for Day 2

Author: kfarnung

2024/day02/main.go

@@ -0,0 +1,115 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"slices"
+	"strings"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+)
+
+func part1(input string) int64 {
+	reports, err := parseInput(input)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	count := int64(0)
+	for _, report := range reports {
+		if isSafeReport(report) {
+			count++
+		}
+
+		slices.Reverse(report)
+
+		if isSafeReport(report) {
+			count++
+		}
+	}
+
+	return count
+}
+
+func part2(input string) int64 {
+	reports, err := parseInput(input)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	count := int64(0)
+	for _, report := range reports {
+		if isSafeReportAllowOneSkip(report) {
+			count++
+		}
+	}
+
+	return count
+}
+
+func isSafeReportAllowOneSkip(report []int64) bool {
+	for i := 0; i < len(report); i++ {
+		backup := report[i]
+		report = slices.Delete(report, i, i+1)
+		if isSafeReport(report) {
+			return true
+		}
+
+		slices.Reverse(report)
+		if isSafeReport(report) {
+			return true
+		}
+
+		slices.Reverse(report)
+		report = slices.Insert(report, i, backup)
+	}
+
+	return false
+}
+
+func isSafeReport(report []int64) bool {
+	for i := 1; i < len(report); i++ {
+		if report[i] <= report[i-1] || report[i]-report[i-1] > 3 {
+			return false
+		}
+	}
+
+	return true
+}
+
+func parseInput(input string) ([][]int64, error) {
+	var reports [][]int64
+
+	for _, line := range lib.SplitLines(input) {
+		if line == "" {
+			continue
+		}
+
+		var levels []int64
+		numbers := strings.Split(line, " ")
+		for _, number := range numbers {
+			num, err := lib.ParseInt[int64](number)
+			if err != nil {
+				return nil, err
+			}
+
+			levels = append(levels, num)
+		}
+
+		reports = append(reports, levels)
+	}
+
+	return reports, nil
+}
+
+func main() {
+	name := os.Args[1]
+	content, err := lib.LoadFileContent(name)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("Part 1: %d\n", part1(content))
+	fmt.Printf("Part 2: %d\n", part2(content))
+}

2024/day02/main_test.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+	"github.com/stretchr/testify/assert"
+)
+
+var input = strings.Join([]string{
+	"7 6 4 2 1",
+	"1 2 7 8 9",
+	"9 7 6 2 1",
+	"1 3 2 4 5",
+	"8 6 4 4 1",
+	"1 3 6 7 9",
+}, "\n")
+
+func TestPart1(t *testing.T) {
+	assert.Equal(t, int64(2), part1(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(411), part1(inputContent))
+}
+
+func TestPart2(t *testing.T) {
+	assert.Equal(t, int64(4), part2(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(465), part2(inputContent))
+}