Get a unique list of items that occur more than once in a list

Question

I have a list of items:

mylist = [\'A\',\'A\',\'B\',\'C\',\'D\',\'E\',\'D\']

I want to return a unique list of items that appear more than

Answer 1

Might not be as fast as internal implementations, but takes (almost) linear time (since set lookup is logarithmic)

mylist = ['A','A','B','C','D','E','D']
myset = set()
dups = set()
for x in mylist:
    if x in myset:
        dups.add(x)
    else:
        myset.add(x)
dups = list(dups)
print dups