bug: Fixing day4 solution

Author: truggeri

src/day4/day4.go

@@ -3,153 +3,53 @@ package day4
 import (
 	"slices"
 	"strings"
-	"unicode/utf8"
 )
 
-const WORD_TO_FIND = "XMAS"
-
-var _rows []string
+type strategy func([][]rune, int, int) bool
 
 func Solve(input string) uint {
-	_rows = make([]string, 0)
-	return matchesByStrategy(input, rows) + matchesByStrategy(input, columns) + matchesByStrategy(input, diagonals)
-}
-
-func matchesByStrategy(input string, strategy func(string) []string) uint {
-	var count uint = 0
-	for _, x := range strategy(input) {
-		if contains(x) {
-			count += 1
-		}
-		if contains(reverse(x)) {
-			count += 1
-		}
-	}
-	return count
-}
-
-func contains(input string) bool {
-	return strings.Contains(input, WORD_TO_FIND)
-}
-
-func rows(input string) []string {
-	if len(_rows) == 0 {
-		_rows = strings.Split(input, "\n")
-	}
-	return _rows
-}
-
-func columns(input string) []string {
-	rows := rows(input)
-	var cols []string = make([]string, len(rows))
-	for _, r := range rows {
-		for j, v := range r {
-			if j >= len(rows) {
-				panic("The input puzzle is not square")
+	puzzle := parseInput(input)
+	ss := []strategy{builder(0, -1), builder(0, 1), builder(-1, 0), builder(1, 0), builder(-1, -1), builder(1, -1), builder(-1, 1), builder(1, 1)}
+	var result uint = 0
+	for j, line := range puzzle {
+		for i := range line {
+			for _, s := range ss {
+				if s(puzzle, i, j) {
+					result++
+				}
 			}
-			cols[j] += string(v)
 		}
 	}
-	return cols
-}
-
-func diagonals(input string) []string {
-	rows := rows(input)
-	wordSize := len(WORD_TO_FIND)
-	squareSize := len(rows)
-	var diagonals []string = make([]string, 0)
-	seed := squareSize - wordSize
-
-	for s := 0; s <= seed; s++ {
-		buf1 := forwardLower(s, squareSize, rows)
-		buf2 := forwardUpper(s, squareSize, rows)
-		buf3 := backLower(s, squareSize, rows)
-		buf4 := backUpper(s, squareSize, rows)
-		diagonals = slices.Insert(diagonals, len(diagonals), string(buf1), string(buf2), string(buf3), string(buf4))
-	}
-
-	return diagonals
+	return result
 }
 
-func forwardLower(s int, squareSize int, rows []string) []byte {
-	buf := make([]byte, 0)
-	i := 0
-	j := s
-	for {
-		if !inPuzzle(i, j, squareSize) {
-			break
+func parseInput(input string) [][]rune {
+	result := make([][]rune, 0)
+	for j, line := range strings.Split(input, "\n") {
+		result = slices.Insert(result, j, make([]rune, 0))
+		for _, r := range line {
+			result[j] = append(result[j], r)
 		}
-
-		buf = slices.Insert(buf, len(buf), rows[i][j])
-		i++
-		j++
 	}
-	return buf
+	return result
 }
 
-func forwardUpper(s int, squareSize int, rows []string) []byte {
-	buf := make([]byte, 0)
-	if s == 0 {
-		return buf
-	}
-	i := s
-	j := 0
-	for {
-		if !inPuzzle(i, j, squareSize) {
-			break
+func builder(right, up int) strategy {
+	word := [4]rune{'X', 'M', 'A', 'S'}
+	length := len(word)
+	return func(puzzle [][]rune, x, y int) bool {
+		if (up < 0 && y < length-1) || (up > 0 && y > len(puzzle)-length) {
+			return false
 		}
-
-		buf = slices.Insert(buf, len(buf), rows[i][j])
-		i++
-		j++
-	}
-	return buf
-}
-
-func backUpper(s int, squareSize int, rows []string) []byte {
-	buf := make([]byte, 0)
-	i := squareSize - 1 - s
-	j := 0
-	for {
-		if !inPuzzle(i, j, squareSize) {
-			break
+		if (right < 0 && x < length-1) || (right > 0 && x > len(puzzle)-length) {
+			return false
 		}
 
-		buf = slices.Insert(buf, len(buf), rows[i][j])
-		i--
-		j++
-	}
-	return buf
-}
-
-func backLower(s int, squareSize int, rows []string) []byte {
-	buf := make([]byte, 0)
-	i := squareSize - 1
-	j := s
-	for {
-		if !inPuzzle(i, j, squareSize) {
-			break
+		for i, r := range word {
+			if puzzle[y+(i*up)][x+(i*right)] != r {
+				return false
+			}
 		}
-
-		buf = slices.Insert(buf, len(buf), rows[i][j])
-		i--
-		j++
-	}
-	return buf
-}
-
-// @see {https://stackoverflow.com/a/34521190}
-func reverse(s string) string {
-	size := len(s)
-	buf := make([]byte, size)
-	for start := 0; start < size; {
-		r, n := utf8.DecodeRuneInString(s[start:])
-		start += n
-		utf8.EncodeRune(buf[size-start:], r)
+		return true
 	}
-	return string(buf)
-}
-
-func inPuzzle(i, j int, squareSize int) bool {
-	return i >= 0 && i < squareSize && j >= 0 && j < squareSize
 }