aoc2024/internal/day04/handler.go

package day04

import (
	"errors"
)

var ErrNotEnoughSpace = errors.New("not enough space to form word")

func Handle(input []string) (int, int) {
	xmas := 0
	crossMAS := 0
	for i, line := range input {
		for j, char := range line {
			if char == 'X' {
				xmas += countWord(input, "XMAS", i, j)
			}
			if char == 'A' {
				crossMAS += countCrossPattern(input, "MAS", i, j)
			}
		}
	}
	return xmas, crossMAS
}

func countWord(matrix []string, word string, posY, posX int) int {
	wordCount := 0
	wordLenght := len(word)
	result, err := getWordHoz(matrix, wordLenght, posY, posX)
	if err == nil && result == word {
		wordCount++
	}
	result, err = getWordHozRev(matrix, wordLenght, posY, posX)
	if err == nil && result == word {
		wordCount++
	}
	result, err = getWordVert(matrix, wordLenght, posY, posX)
	if err == nil && result == word {
		wordCount++
	}
	result, err = getWordVertRev(matrix, wordLenght, posY, posX)
	if err == nil && result == word {
		wordCount++
	}
	result, err = getWordDiagAsc(matrix, wordLenght, posY, posX)
	if err == nil && result == word {
		wordCount++
	}
	result, err = getWordDiagAscRev(matrix, wordLenght, posY, posX)
	if err == nil && result == word {
		wordCount++
	}
	result, err = getWordDiagDesc(matrix, wordLenght, posY, posX)
	if err == nil && result == word {
		wordCount++
	}
	result, err = getWordDiagDescRev(matrix, wordLenght, posY, posX)
	if err == nil && result == word {
		wordCount++
	}

	return wordCount
}

func countCrossPattern(matrix []string, word string, posY, posX int) int {
	wordCount := 0
	wordLenght := len(word)

	result, err := getWordDiagAsc(matrix, wordLenght, posY-1, posX-1)
	if err == nil && result == word {
		wordCount++
	}
	result, err = getWordDiagAscRev(matrix, wordLenght, posY-1, posX+1)
	if err == nil && result == word {
		wordCount++
	}
	result, err = getWordDiagDesc(matrix, wordLenght, posY+1, posX-1)
	if err == nil && result == word {
		wordCount++
	}
	result, err = getWordDiagDescRev(matrix, wordLenght, posY+1, posX+1)
	if err == nil && result == word {
		wordCount++
	}

	if wordCount == 2 {
		return 1
	}
	return 0
}

func reverseString(str string) string {
	runes := []rune(str)
	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
		runes[i], runes[j] = runes[j], runes[i]
	}
	return string(runes)
}

func getWordHoz(matrix []string, wordLenght, posY, posX int) (string, error) {
	if posX > len(matrix[posY])-wordLenght {
		return "", ErrNotEnoughSpace
	}
	if posX > len(matrix[posY])-wordLenght-1 {
		return string(matrix[posY][posX:]), nil
	}
	return string(matrix[posY][posX : posX+wordLenght]), nil
}

func getWordHozRev(matrix []string, wordLenght, posY, posX int) (string, error) {
	if posX < wordLenght-1 {
		return "", ErrNotEnoughSpace
	}
	if posX < wordLenght {
		word := matrix[posY][0:wordLenght]
		return reverseString(word), nil
	}
	return reverseString(matrix[posY][posX-wordLenght+1 : posX+1]), nil
}

func getWordVert(matrix []string, wordLenght, posY, posX int) (string, error) {
	if posY > len(matrix)-wordLenght {
		return "", ErrNotEnoughSpace
	}
	word := make([]byte, wordLenght)
	for i := 0; i < wordLenght; i++ {
		word[i] = matrix[posY+i][posX]
	}
	return string(word), nil
}

func getWordVertRev(matrix []string, wordLenght, posY, posX int) (string, error) {
	if posY < wordLenght-1 {
		return "", ErrNotEnoughSpace
	}
	word := make([]byte, wordLenght)
	for i := 0; i < wordLenght; i++ {
		word[i] = matrix[posY-i][posX]
	}
	return string(word), nil
}

func getWordDiagAsc(matrix []string, wordLenght, posY, posX int) (string, error) {
	if posY > len(matrix)-wordLenght || posX > len(matrix[posY])-wordLenght {
		return "", ErrNotEnoughSpace
	}

	word := make([]byte, wordLenght)
	for i := 0; i < wordLenght; i++ {
		word[i] = matrix[posY+i][posX+i]
	}
	return string(word), nil
}

func getWordDiagAscRev(matrix []string, wordLenght, posY, posX int) (string, error) {
	if posY > len(matrix)-wordLenght || posX < wordLenght-1 {
		return "", ErrNotEnoughSpace
	}

	word := make([]byte, wordLenght)
	for i := 0; i < wordLenght; i++ {
		word[i] = matrix[posY+i][posX-i]
	}
	return string(word), nil
}

func getWordDiagDesc(matrix []string, wordLenght, posY, posX int) (string, error) {
	if posY < wordLenght-1 || posX > len(matrix[posY])-wordLenght {
		return "", ErrNotEnoughSpace
	}

	word := make([]byte, wordLenght)
	for i := 0; i < wordLenght; i++ {
		word[i] = matrix[posY-i][posX+i]
	}

	return string(word), nil
}

func getWordDiagDescRev(matrix []string, wordLenght, posY, posX int) (string, error) {
	if posY < wordLenght-1 || posX < wordLenght-1 {
		return "", ErrNotEnoughSpace
	}

	word := make([]byte, wordLenght)
	for i := 0; i < wordLenght; i++ {
		word[i] = matrix[posY-i][posX-i]
	}
	return string(word), nil
}