Printing all combinations from a set of sets

theTinker

If i was to print out all combinations of multiple sets of items, it would look like this. But This needs to know how many sets there are.

set1[1,2,3]
set2[A,B,C]
set3[X,Y,Z]

for set1 - i
{ 
for set2 - y
{
for set3 - t
{
print set1[i] set2[y] set3[t]
}
}
}

Would this solution work for unknown number of sets(less than 20 so efficency isnt a problem). Its my first recursive but i think it would work.

HistoricValue = " "

Function(HistoricValue,Sets)
{
	if(Sets.length != 0){
		SingleSet = Sets[0]
		
		For each i in SingleSet {
			
			var currentValue = HistoricValue + " " + SingleSet[i];

			function(currentValue,Sets.subSet(1,Sets.length));
                }
	 }else{
		print HistoricalValue
	 }
}

I've no compiler or dev system on this slow laptop!

Tillotson

Something like that should work alright. Just make sure "HistoricValue" doesn't have global scope. Might be better to rename to HistoricValue to currentVal and currentVal to nextVal.

I decided to just go ahead and do it in Haskell:

fun = go []
    where
      go acc xss
          | length xss == 0 = [acc]
          | otherwise = concatMap (\x -> go (acc++[x]) (tail xss)) $ head xss

-- fun ["ab", "CDEF", "x"] == ["aCx","aDx","aEx","aFx","bCx","bDx","bEx","bFx"]

Another way to think of the problem would be to think of each "Set" as a ring on a combination lock and apply rotations to the rings. The code would probably be 3x as long and it might be difficult to deal with uneven sized "Sets".

I occasionally use a 6+yr old laptop to program. Unless you're stuck using a Visual Studio / Eclipse you should be alright getting started on just about anything.

If you're interested in programming/maths problems you should check out projecteuler.net