Right... basically every solution that's using the "+111" or "i * 111" hack would miss 000.

Test cases can't be edited anymore, more than 500 people have completed it :( Thanks for pointing out missing test case, would have loved to add it.

I was about to open an issue, too, but I think I meant the same, so I'll just comment here:

The hardcoded test cases should include something like: TripleDouble(111L, 22L), which should return 0, because the digit is not the same in the triple and double.

Although there are random test cases, they do not necessarily cover this case and some incorrect solutions pass.