Bloom filter in Java

Question

Basically I have to implement a bloom filter and test it with char 'a' to 'z' and 'A' to 'Z' (easy and done).

Then I have to test for false positives but the requirements say to use "aa" to "ZZ" (strings) to count the false positives (not done).

Any idea what that means?

Answer 1

false positive requires actual set of data, I think what your professor meant was: add 'a'-'z','A'-'Z' to the filter (actual data) now, check for all the strings "aa"-"ZZ", count the number of false positives (all positives will be false, since none of them are in the data) and extract the ratio: #false_positives/#strings_in_range("aa","ZZ")

EDIT: at comments @Bill asked how to iterate over "aa"-"ZZ", here is a simple code snap of how to do it.

Set<String> set = new HashSet<String>();
for (Character c = 'a';c<='z';c++) { 
     String lower = c.toString();
     String upper = c.toString().toUpperCase();
     for (Character k = 'a';k<='z';k++) { 
            set.add(lower + k.toString());
            set.add(lower + k.toString().toUpperCase());
            set.add(upper + k.toString());
            set.add(upper + k.toString().toUpperCase());
     }
}