Reporting where values match and mismatch across three columns

Hello,
I have values in three columns. Some values occur in all three columns, other values are present in only one or two columns. I would like to be able to see where the matches and mismatches occur. Thanks in advance for any advice!

I have:

A B C
1 1 2
2 3 3
3 4 5
4 6
5

I would like:

A B C
1 1 X
2 X 2
3 3 3
4 4 X
5 X 5
X X 6