You should use the BigDecimal class instead of double here, since exact precision of the floating point numbers in your array adding up to 0 is a must for your solution. If one of your decimal values was .1, you're in trouble. That binary fraction cannot be precisely represented with a double. Take the following code as an example:
double counter = 0.0;
while (counter != 1.0)
{
System.out.println("Counter = " + counter);
counter = counter + 0.1;
}
You would expect this to execute 10 times, but it is an infinite loop since counter will never be precisely 1.0.
Example output:
Counter = 0.0
Counter = 0.1
Counter = 0.2
Counter = 0.30000000000000004
Counter = 0.4
Counter = 0.5
Counter = 0.6
Counter = 0.7
Counter = 0.7999999999999999
Counter = 0.8999999999999999
Counter = 0.9999999999999999
Counter = 1.0999999999999999
Counter = 1.2
Counter = 1.3
Counter = 1.4000000000000001
Counter = 1.5000000000000002
Counter = 1.6000000000000003
When you search for either pairs or an individual element, you need to count with multiplicity. I.e., if you find element -d in your array of either singletons or pairs, then you need to increase the count by the number of matches that are found, not just increase by 1. This is probably why you're not getting the full number of results when you search over pairs. And it could mean that the number 528 of matches is not the true full number when you are searching over singletons. And in general, you should not use double precision arithmetic for exact arithmetic; use an arbitrary precision rational number package instead.
출처
https://stackoverflow.com/questions/22079815