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.