Re: Algorithm to find pairs in array [can not order]
Hello, so I am trying to make a better (with less complexity,
prefferably without a nested loop) to find something like pairs of
items in an ArrayList:
So far I've got this:
// shuffle Option offers
for (int i=0;i<offeredOptions.size()-1;i++)
Offer of1 = offeredOptions.get(i);
// look for a matching option offer in the list
for (int j=1;j<offeredOptions.size();j++)
Offer of2 = offeredOptions.get(j);
/* we are looking for 2 offers for the same Option contract with
* offer types (write and hold)
if (of1.getOption() == of1.getOption() &&
(of1.type == OfferType.hold && of2.type == OfferType.write) ||
(of1.type == OfferType.write && of2.type == OfferType.hold))
// do something else
break; // get to the
I know it is not optimal, but basically I need to match 2 items from
the array (which is randomized), and then remove them.
I am sure there must be a more efficient way to do this but I cant
remember the proper algorithm...
I know it is not a *proper* Java question but didn't knew which group
There is a quick halving of the work. The inner loop does not need to
begin from index 1. It can start from i+1, because any match between a
pair either of which has an index value less than i would have been
found on a previous outer loop iteration.
If you rely on direct comparison, using the unordered array, the work is
going to be O(n*n).
What is the type of a getOption() result? Can there be more than two
offers with the same contract?
Depending on those answers, there may be much more efficient solutions
for large n in which the data gets copied to a HashSet or HashMap during
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