Scottrade has some examples on their website that cover this (I'm not sure if a link to it is permitted here but a quick search should let you find it).
Scenario B is not a wash sale as you've closed out your position and there are no "replacement shares".
For scenario A, it depends on whether the initial 300 share purchase was one transaction or more than one. If one transaction, then not a wash sale as there are no "replacement shares". But if more than one transaction (e.g. you bought 100, then 200 more), then it is a wash sale as that initial buy of 100 would be considered the "replacement shares".
What this ends up meaning (although I've not heard it put this way before) is that there can not be a wash sale until there have been at least two separate purchases (one considered the original purchase and one considered the purchase of the "replacement shares").
