[2024] Solution for Day 4

Author: kfarnung

2024/day04/main.go

@@ -0,0 +1,128 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+)
+
+var xmasString []rune = []rune("XMAS")
+
+func part1(input string) int64 {
+	parsedInput := parseInput(input)
+	count := int64(0)
+	for x, line := range parsedInput {
+		for y, char := range line {
+			if char != 'X' {
+				continue
+			}
+
+			if findXmas(parsedInput, x, y, 1, 0) {
+				count++
+			}
+
+			if findXmas(parsedInput, x, y, 0, 1) {
+				count++
+			}
+
+			if findXmas(parsedInput, x, y, 1, 1) {
+				count++
+			}
+
+			if findXmas(parsedInput, x, y, 1, -1) {
+				count++
+			}
+
+			if findXmas(parsedInput, x, y, -1, 0) {
+				count++
+			}
+
+			if findXmas(parsedInput, x, y, 0, -1) {
+				count++
+			}
+
+			if findXmas(parsedInput, x, y, -1, -1) {
+				count++
+			}
+
+			if findXmas(parsedInput, x, y, -1, 1) {
+				count++
+			}
+		}
+	}
+
+	return count
+}
+
+func part2(input string) int64 {
+	parsedInput := parseInput(input)
+	count := int64(0)
+	for x, line := range parsedInput {
+		for y, char := range line {
+			if char != 'A' {
+				continue
+			}
+
+			if x == 0 || y == 0 || x == len(parsedInput)-1 || y == len(parsedInput[x])-1 {
+				continue
+			}
+
+			if parsedInput[x-1][y-1] == 'M' && parsedInput[x+1][y+1] == 'S' && parsedInput[x-1][y+1] == 'M' && parsedInput[x+1][y-1] == 'S' {
+				count++
+			}
+
+			if parsedInput[x-1][y-1] == 'M' && parsedInput[x+1][y+1] == 'S' && parsedInput[x-1][y+1] == 'S' && parsedInput[x+1][y-1] == 'M' {
+				count++
+			}
+
+			if parsedInput[x-1][y-1] == 'S' && parsedInput[x+1][y+1] == 'M' && parsedInput[x-1][y+1] == 'S' && parsedInput[x+1][y-1] == 'M' {
+				count++
+			}
+
+			if parsedInput[x-1][y-1] == 'S' && parsedInput[x+1][y+1] == 'M' && parsedInput[x-1][y+1] == 'M' && parsedInput[x+1][y-1] == 'S' {
+				count++
+			}
+		}
+	}
+
+	return count
+}
+
+func findXmas(parsedInput [][]rune, x, y int, dx, dy int) bool {
+	for i := 0; i < len(xmasString); i++ {
+		if x < 0 || x >= len(parsedInput) || y < 0 || y >= len(parsedInput[x]) || parsedInput[x][y] != xmasString[i] {
+			return false
+		}
+
+		x += dx
+		y += dy
+	}
+
+	return true
+}
+
+func parseInput(input string) [][]rune {
+	var result [][]rune
+	for _, line := range lib.SplitLines(input) {
+		if len(line) == 0 {
+			continue
+		}
+
+		result = append(result, []rune(line))
+	}
+
+	return result
+}
+
+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/day04/main_test.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+	"github.com/stretchr/testify/assert"
+)
+
+var input = strings.Join([]string{
+	"MMMSXXMASM",
+	"MSAMXMSMSA",
+	"AMXSXMAAMM",
+	"MSAMASMSMX",
+	"XMASAMXAMM",
+	"XXAMMXXAMA",
+	"SMSMSASXSS",
+	"SAXAMASAAA",
+	"MAMMMXMMMM",
+	"MXMXAXMASX",
+	"",
+}, "\n")
+
+func TestPart1(t *testing.T) {
+	assert.Equal(t, int64(18), part1(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(2583), part1(inputContent))
+}
+
+func TestPart2(t *testing.T) {
+	assert.Equal(t, int64(9), part2(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(1978), part2(inputContent))
+}