Simple problems resolved

Good morning!

I added the files with the solutions.
They were created in Visual Studio 2010.

Here is a print screen of the VS Solution if you want to reproduce it:
![vs_solution](https://cloud.githubusercontent.com/assets/8064846/3478786/0748603c-0344-11e4-9cd8-14a79bd121ac.png)

The UnitTests project needs a reference to the SimpleProblems project.

Thank you for your time.
Why are the calls to Math.Abs necessary? Can the value be negative? 
Why do you use a multiplication to mark the number/position as visited? Wouldn't just setting it to -1 work?