Check initial grid availability for backtracking/sudoku.py

[RonDingDing]

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 original code above if you change the number 9 in the fifth line to 5, you will have a solution. But that is not a valid sudoku according to the definition. That means it's not validating whether the origingal sudoku can be solved. Not to mention to put a 10 anywhere or a minus number or a float at initial matrix. In the current request, this bug is fixed.

[TravisBuddy]

Travis tests have failed

Hey @RonDingDing,
Please read the following log in order to understand the failure reason.
It'll be awesome if you fix what's wrong and commit the changes.

TravisBuddy Request Identifier: 2eaa63e0-1a95-11eb-ae00-6f9b88d90b9e

[TravisBuddy]

Travis tests have failed

Hey @RonDingDing,
Please read the following log in order to understand the failure reason.
It'll be awesome if you fix what's wrong and commit the changes.

TravisBuddy Request Identifier: 51ba80b0-1afc-11eb-ae51-b75871e10011

[TravisBuddy]

Hey @RonDingDing,
Something went wrong with the build.

TravisCI finished with status errored, which means the build failed because of something unrelated to the tests, such as a problem with a dependency or the build process itself.

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TravisBuddy Request Identifier: 1165a5e0-1b50-11eb-ae51-b75871e10011

[TravisBuddy]

Hey @RonDingDing,
Something went wrong with the build.

TravisCI finished with status errored, which means the build failed because of something unrelated to the tests, such as a problem with a dependency or the build process itself.

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TravisBuddy Request Identifier: 838865e0-1b50-11eb-ae51-b75871e10011