What I'd do is sort the popular passwords by length, start with the longest. Then as you're adding new passwords to the end, check if it's already in there. T

What I'd do is sort the popular passwords by length, start with the longest. Then as you're adding new passwords to the end, check if it's already in there. Then you'll go from phrases to words with a lot of them being duplicates. At least if you wanted to keep it as a long string. I'd still probably approach this as a bloom filter as others suggested since it'd let you have a larger number of entries for similar memory footprint.