title: How to swap `NSMutableDictionary` key and values in place?
body: <p>I have a <code>NSMutableDictionary</code> and I want to swap values &amp; keys. i.e, after swapping values becomes keys and its corresponding keys with become values  All keys and values are unique. Looking for an in place solution because size is very big . Also, the keys and values are <code>NSString</code> objects </p>