Unique hash for same set of characters given in any order?

Question

Consider this example of finding anagrams

aabc
abca

They both are anagrams, I am looking for a way so that their hash generated by characters is same and unique.

The uniqueness is important so that no two different string aabc and xyaq generate the same hash

I have no idea about this, but throwing up here to learn what I need to look up for

Answer 1

Sort the characters in the string and use that as the hash. Strings will have the same hash if they are anagrams of each other:

String anagramHash(String str) {
    char[] chars = str.toCharArray();
    Arrays.sort(chars);
    return new String(chars);
}

This probably won't work if you have code points which aren't on the BMP (http://docs.oracle.com/javase/7/docs/api/java/lang/Character.html).

Alternatively, generate a histogram and use that as the hash.