Valid Sudoku · Interview Problem

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Valid Sudoku

Check whether a partially filled $9\times 9$ Sudoku board satisfies all Sudoku rules.

Acceptance 100%

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Problem Statement

You are given a partially filled $9 \times 9$ Sudoku board. Some cells contain digits from 1 to 9, and empty cells are marked with '.'.

Determine whether the current board configuration is valid.

A valid Sudoku board must satisfy all of the following rules:

Each row contains no duplicate digits from 1 to 9.
Each column contains no duplicate digits from 1 to 9.
Each of the nine $3 \times 3$ sub-boxes contains no duplicate digits from 1 to 9.

Only the filled cells need to be checked; the board does not need to be solvable.

Input Format

A $9 \times 9$ grid of characters.
Each cell is either a digit from 1 to 9 or '.' for empty.

Output Format

Return true if the board is valid according to Sudoku rules.
Otherwise, return false.

Constraints

The board size is fixed at $9 \times 9$ .
Empty cells marked '.' should be ignored.
Digits are limited to 1 through 9.

Examples

Sample cases returned by the problem API.

Example 1

Input

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"]
]

Output

true

Explanation

No row, column, or 3x3 sub-box contains duplicate filled digits.

Example 2

Input

board = [
  ["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

The digit 8 appears twice in the first column, so the board is invalid.

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