Algorithm - How to delete duplicate elements in a list efficiently?

Question

There is a list L. It contains elements of arbitrary type each. How to delete all duplicate elements in such list efficiently? ORDE

Answer 1

• go through the list and assign sequential index to each item
• sort the list basing on some comparison function for elements
• remove duplicates
• sort the list basing on assigned indices

for simplicity indices for items may be stored in something like std::map

looks like O(n*log n) if I haven't missed anything