//Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules. (http://sudoku.com.au/TheRules.aspx)

//The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

//A partially filled sudoku which is valid.

//Note:

//A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.

class ValidSudoku {

public boolean isValidSudoku(char[][] board) {

for(int i = 0; i < board.length; i++){

HashSet<Character> rows = new HashSet<Character>();

HashSet<Character> columns = new HashSet<Character>();

HashSet<Character> box = new HashSet<Character>();

for (int j = 0; j < board[0].length; j++){

if(board[i][j] != '.' && !rows.add(board[i][j])) {

return false;

}

if(board[j][i]!='.' && !columns.add(board[j][i])) {

return false;

}

int rowIndex = (i / 3) * 3;

int columnIndex = (i % 3) * 3;

if(board[rowIndex + j / 3][columnIndex + j % 3] != '.' && !box.add(board[rowIndex + j / 3][columnIndex + j % 3])) {

return false;

}

}

}

return true;

}

}