I love that this one puzzle has two possible solutions:

This problem can be solved by pre-school children in 5-10 minutes, by programer – in 1 hour, by people with higher education … well, check it yourself!

8809=6
7111=0
2172=0
6666=4
1111=0
3213=0
7662=2
9313=1
0000=4
2222=0
3333=0
5555=0
8193=3
8096=5
7777=0
9999=4
7756=1
6855=3
9881=5
5531=0
2581=?

See if you can figure out both possible solutions.

Jamie is a .NET developer specialising in ASP.NET MVC websites and services, with a background in WinForms and Games Development. When not programming using .NET, he is either learning about .NET Core (and usually building something cross platform with it), speaking Japanese to anyone who'll listen, learning about languages, writing for this blog, or writing for a blog about Retro Gaming (which he runs with his brother)