Problem Statement

Determine if a 9x9 Sudoku board is valid. A valid Sudoku board will hold the following conditions:

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

Note:

1. The Sudoku board could be partially filled, where empty cells are filled with the character '.'.
2. You need to validate only filled cells.

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"]]
  

• Expected Output: true
• Justification: This Sudoku board is valid as it adheres to the rules of no repetition in each row, each column, and each 3x3 sub-box.

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"]]
  

• Expected Output: false
• Justification: The first and fourth rows both contain the number '8', violating the Sudoku rules.

Example 3:

• Input:

  [[".",".","4",".",".",".","6","3","."]
  ,[".",".",".",".",".",".",".",".","."]
  ,["5",".",".",".",".",".",".","9","."]
  ,[".",".",".","5","6",".",".",".","."]
  ,["4",".","3",".",".",".",".",".","1"]
  ,[".",".",".","7",".",".",".",".","."]
  ,[".",".",".","5",".",".",".",".","."]
  ,[".",".",".",".",".",".",".",".","."]
  ,[".",".",".",".",".",".",".",".","."]]
  

• Expected Output: false
• Justification: The fourth column contains the number '5' two times, violating the Sudoku rules.

Constraints:

• board.length == 9
• board[i].length == 9
• board[i][j] is a digit 1-9 or '.'.

Try it yourself

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