Check initial grid availability for backtracking/sudoku.py

[RonDingDing]

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

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• This pull request is all my own work -- I have not plagiarized.
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initial_grid = [
    [3, 0, 6, 5, 0, 8, 4, 0, 0],
    [5, 2, 0, 0, 0, 0, 0, 0, 0],
    [0, 8, 7, 0, 0, 0, 0, 3, 1],
    [0, 0, 3, 0, 1, 0, 0, 8, 0],
    [9, 0, 0, 8, 6, 3, 0, 0, 5],
    [0, 5, 0, 0, 9, 0, 6, 0, 0],
    [1, 3, 0, 0, 0, 0, 2, 5, 0],
    [0, 0, 0, 0, 0, 0, 0, 7, 4],
    [0, 0, 5, 2, 0, 6, 3, 0, 0],
]

In the previous code, if you change 9 at the fifth line to 5, the program will give you a solution. But the output does not conform to the definition of sudoku. It means the program is not checking the input at all. So I add some validation of the input, specifying the grid to be 9*9 2D-list of 0-9.

[RonDingDing]

???

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[RonDingDing]

??