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

Compact and exact

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.