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# Validate a Sudoku
## Definition
Sudokus are number-puzzles in which cells in a 9×9 grid must be populated with the numbers `1` to `9`.
The following constraints must apply to the 9×9 grid.
* Each digit from `1` to `9` only occurs only once
* per row
* per column
* per block (i.e. 3×3 sub grid)
## Goal
Validate, if a given Sudoku is a valid solution.
The Sudoku must comply with the definition above.
### Input
A sequence of 81 digits, organized in 9 columns and 9 rows.
The columns of a row are separated by blanks.
Rows are separated by line-breaks.
### Output
A boolean value `true` or `false` defining the correctness of the input.