How to get rid of duplicates in a list, but keep the order

Question

I am using Intermediate Student with Lambda in DrRacket, I was wondering how one would remove the duplicates in a list, while keeping the order. For example (remo

Answer 1

Run through the list sequentially, inserting each element in a hash table or other dictionary. If you try to insert an element that is already in the hash table, do not add it to the outgoing list.