But it is mentioned to not store Cats reference since it interrupts garbage collection.

Compact and exact

The tests are randomly shuffled, but they are ok. Both tests expects false if you don't get why, read the instructions again.

JavaScript Completions 4186

I found an issue with fourth test case with JS.

This is the input array:
Here's the board I'm getting;
[ [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ],
[ 2, 3, 1, 5, 6, 4, 8, 9, 7 ],
[ 3, 1, 2, 6, 4, 5, 9, 7, 8 ],
[ 4, 5, 6, 7, 8, 9, 1, 2, 3 ],
[ 5, 6, 4, 8, 9, 7, 2, 3, 1 ],
[ 6, 4, 5, 9, 7, 8, 3, 1, 2 ],
[ 7, 8, 9, 1, 2, 3, 4, 5, 6 ],
[ 8, 9, 7, 2, 3, 1, 5, 6, 4 ],
[ 9, 7, 8, 3, 1, 2, 6, 4, 5 ] ]

But the test is being run on the array below:

1 2 3 4 5 6 7 8 9,
1 2 3 4 5 6 7 8 9,
1 2 3 4 5 6 7 8 9,
1 2 3 4 5 6 7 8 9,
1 2 3 4 5 6 7 8 9,
1 2 3 4 5 6 7 8 9,
1 2 3 4 5 6 7 8 9,
1 2 3 4 5 6 7 8 9,
1 2 3 4 5 6 7 8 9,

I think the test case for fourth one is mixed with the first one

Learnt a lot from your solution.