Strange, I got it working and generating valid solutions locally --- even added a randomizer because there are multiple solutions. But the resolver on the HackRank side does not seem to accept my solutions, like this one:

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