Question

I have a list from 10,000 long value
and I want to compare that data withe 100,000 other long value
compare is a bitwise operation –>

if (a&b==a) count++;

which algoritm I can use for getting best performance?

Answer 1

If I understand your question correctly, you want to check a against each b whether some predicate is true. So a naive solution to your problem would be as follows:

var result = aList.Sum(a => bList.Count(b => (a & b) == a));

I’m not sure this can really be sped up for an arbitrary predicate, because you can’t get around checking each a against each b. What you could try is run the query in parallel:

var result = aList.AsParallel().Sum(a => bList.Count(b => (a & b) == a));

Example:

aList: 10,000 random long values; bList: 100,000 random long values.

• without AsParallel: 00:00:13.3945187

• with AsParallel: 00:00:03.8190386