36. Valid Sudoku

Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

1. Each row must contain the digits 1-9 without repetition.
2. Each column must contain the digits 1-9 without repetition.
3. Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition.

A partially filled sudoku which is valid.

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

Example 1:

Input:
[
  ["5","3",".",".","7",".",".",".","."],
  ["6",".",".","1","9","5",".",".","."],
  [".","9","8",".",".",".",".","6","."],
  ["8",".",".",".","6",".",".",".","3"],
  ["4",".",".","8",".","3",".",".","1"],
  ["7",".",".",".","2",".",".",".","6"],
  [".","6",".",".",".",".","2","8","."],
  [".",".",".","4","1","9",".",".","5"],
  [".",".",".",".","8",".",".","7","9"]
]
Output: true

Example 2:

Input:
[
  ["8","3",".",".","7",".",".",".","."],
  ["6",".",".","1","9","5",".",".","."],
  [".","9","8",".",".",".",".","6","."],
  ["8",".",".",".","6",".",".",".","3"],
  ["4",".",".","8",".","3",".",".","1"],
  ["7",".",".",".","2",".",".",".","6"],
  [".","6",".",".",".",".","2","8","."],
  [".",".",".","4","1","9",".",".","5"],
  [".",".",".",".","8",".",".","7","9"]
]
Output: false
Explanation: Same as Example 1, except with the 5 in the top left corner being 
    modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.
• The given board contain only digits 1-9 and the character '.' .
• The given board size is always 9x9

Solution

(1) Java

class Solution {
    public boolean isValidSudoku(char[][] board) {
        if (board == null || board.length != 9 || board[0].length != 9) {
            return false;
        }
        Set<String> set = new HashSet<>();
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                char c = board[i][j];
                if (c != '.') {
                    if (!set.add(c+"row"+i) ||
                        !set.add(c+"col"+j) ||
                        !set.add(c+"block"+i/3*3+j/3)) {
                        return false;
                    }
                }
            }
        }
        return true;
    }
}

(2) Python

class Solution:
    def isValidSudoku(self, board):
        """
        :type board: List[List[str]]
        :rtype: bool
        """
        if not board or len(board) != 9 or len(board[0]) != 9:
            return False

        for i in range(0,9):
            rSet = set()
            cSet = set()
            for j in range(0, 9):
                c = board[j][i]
                r = board[i][j]
                if r in rSet or c in cSet:
                    return False
                if r != '.':
                    rSet.add(r)
                if c != '.':
                    cSet.add(c)

        for i in range(0, 9, 3):
            for j in range(0, 9, 3):
                xSet = set()
                for k in range(0, 9):
                    x = board[i+int(k/3)][j+int(k%3)];
                    if x == '.':
                        continue
                    if x in xSet:
                        return False
                    xSet.add(x)
        return True

(3) Scala