noodleProblems/
Valid Sudoku
#45

Valid Sudoku

AlgorithmmediumArrayHash TableMatrix

Given a partially filled 9 x 9 Sudoku board, determine whether the currently placed digits are valid. The board uses the strings "1"–"9" for digits and "." for empty cells.

The board is valid when:

- each row contains no repeated digit, - each column contains no repeated digit, - each of the nine 3 x 3 sub-boxes contains no repeated digit.

Only the filled cells are checked — the board does **not** need to be solvable. Return true if valid, false otherwise.

Example cases

  • valid board
    in board =
    53..7....
    6..195...
    .98....6.
    8...6...3
    4..8.3..1
    7...2...6
    .6....28.
    ...419..5
    ....8..79
    out true
    No row, column, or 3x3 box repeats a digit.
  • duplicate in column and box
    in board =
    83..7....
    6..195...
    .98....6.
    8...6...3
    4..8.3..1
    7...2...6
    .6....28.
    ...419..5
    ....8..79
    out false
    Two 8s share the top-left column (and box) — the first column has 8 at rows 0 and 3.

Constraints

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