Oh my bad i thought the instruction said if it contains more than one zero it is invalid.

The last example test expects false, but is a valid solution. If I change the example test to assertTrue, so that i can submit my code and acess the random tests, my code passes all the random tests. absolutley no reason the last grid should return false!

5 3 4 6 7 8 9 1 2
6 7 2 1 9 5 3 4 8
1 9 8 3 4 2 5 6 7
8 5 9 7 6 1 4 2 3
4 2 6 8 0 3 7 9 1
7 1 3 9 2 4 8 5 6
9 6 1 5 3 7 2 8 4
2 8 7 4 1 9 6 3 5
3 4 5 2 8 6 1 7 9