func isValidSudoku(board [][]byte) bool {
var coll, row [9][9]bool
var subBox [3][3][9]bool
for i, rowItem := range board {
for j, cell := range rowItem {
if cell == '.' {
continue
}
charIdx := cell - '1'
if row[i][charIdx] || coll[j][charIdx] || subBox[i/3][j/3][charIdx] {
return false
}
row[i][charIdx] = true
coll[j][charIdx] = true
subBox[i/3][j/3][charIdx] = true
}
}
return true
}