Solve 2024 day 4 in go

2024/go/day-04/main.go

@@ -0,0 +1,106 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+)
+
+func readInput() ([][]rune, error) {
+	content, err := os.ReadFile("input")
+	if err != nil {
+		return nil, err
+	}
+
+	lines := strings.Split(strings.TrimSpace(string(content)), "\n")
+	matrix := make([][]rune, len(lines))
+	for i, line := range lines {
+		matrix[i] = []rune(line)
+	}
+
+	return matrix, nil
+}
+
+func isXmas(word string) bool {
+	return word == "XMAS" || word == "SAMX"
+}
+
+func isMas(word string) bool {
+	return word == "MAS" || word == "SAM"
+}
+
+func countXmas(matrix [][]rune) int {
+	rowCount := len(matrix)
+	colCount := len(matrix[0])
+	var count int
+
+	for rowIndex := 0; rowIndex < rowCount; rowIndex++ {
+		for colIndex := 0; colIndex < colCount; colIndex++ {
+			words := [4]string{}
+
+			// Horizontal word
+			if colIndex < colCount-3 {
+				words[0] = string(matrix[rowIndex][colIndex : colIndex+4])
+			}
+
+			// Vertical word
+			if rowIndex < rowCount-3 {
+				for i := 0; i <= 3; i++ {
+					words[1] += string(matrix[rowIndex+i][colIndex])
+				}
+			}
+
+			// Diagonal words
+			if rowIndex < rowCount-3 && colIndex < colCount-3 {
+				for i := 0; i <= 3; i++ {
+					words[2] += string(matrix[rowIndex+i][colIndex+i])
+					words[3] += string(matrix[rowIndex+(3-i)][colIndex+i])
+				}
+			}
+
+			for _, word := range words {
+				if isXmas(word) {
+					count++
+				}
+			}
+		}
+	}
+
+	return count
+}
+
+func countCrossMas(matrix [][]rune) int {
+	rowCount := len(matrix)
+	colCount := len(matrix[0])
+	var count int
+
+	for rowIndex := 0; rowIndex < rowCount-2; rowIndex++ {
+		for colIndex := 0; colIndex < colCount-2; colIndex++ {
+			var downDiagonalWord, upDiagonalWord string
+
+			for i := 0; i <= 2; i++ {
+				downDiagonalWord += string(matrix[rowIndex+i][colIndex+i])
+				upDiagonalWord += string(matrix[rowIndex+(2-i)][colIndex+i])
+			}
+
+			if isMas(downDiagonalWord) && isMas(upDiagonalWord) {
+				count++
+			}
+		}
+	}
+
+	return count
+}
+
+func main() {
+	matrix, err := readInput()
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	// Part one
+	fmt.Println("Number of XMAS occurrences:", countXmas(matrix))
+	// Part two
+	fmt.Println("Number of X-MAS occurrences:", countCrossMas(matrix))
+}