Add ability to find if the set contains a prefix to the key provided

[wwweert123]

No description provided.

[rklaehn]

Hm, there is also has_prefix and scan_prefix.

has_prefix will return true if the tree has values below the given prefix. scan_prefix will iterate over the entire tree below a prefix. What case does this fn enable that isn't possible with the two mentioned methods?

[wwweert123]

Hi! Instead of checking whether the string provided is a prefix of a key in the set (what is done in has_prefix), the added is_prefix checks whether any keys in the set is a prefix of the string provided.

For example,
radixtree1 = {"www.google.com", "www.youtube.com"}

radixtree1.is_prefix("www.google.com/webhp") will return true