zip codes - Determining which US zipcodes map to more than one state or more than one city?

I'm using a zip code listing, and I am curious to know how many (or which) zip codes map to more than one US state or US city?

For instance I know that Zip Code 42223 resolves to US Army, Fort Campbell which straddles the KY-TN state line. Oddly, the google API only returns TN for that state corresponding to that zip.