I have submitted 36 times and got AC.
If someone is puzzled and I hope I can help you.
1.first,read the problem's hint carefully.
2.If a tomb was visited on day T then its neighbors may be dug over on day T+101.It said "visited",so if a client was buried on day T,and a client could be buried near him on day T+1....It means when a client was buried,he has no last visit,also you can think his last visit is on day -10000.
3.A tomb is dug over as soon as there is an opportunity
Becareful.AS SOON AS.
4.If someone's tomb was not dug,his relatives can visit him successful.
5.Today is T,if a tomb's last visit is before t-1000,and all it's neighbor's last visit is before t-100,it will be dug at once.
So sorry for my poor English.
I hope these can help you.