Digits of $0,1,2,3,\dots ,9$ are written in a cells of a table in case that every digit is written $10$ times (it should be a $10 \times10$ table ). How to prove with working with graph or tree that there must be a row or column that has more than $3 $ different digits?
I tried to solve this with drawing tables but it is not true, actually I could not because I do not know how to solve this problem with graph theory (and how it can be related to). Can you help me solve it in this way?