Array remove duplicate elements

Question

I have an unsorted array, what is the best method to remove all the duplicates of an element if present?

e.g:

a[1,5,2,6,8,9,1,1,10,3,2,4,1,3,11,3]
         


        

Answer 1

This can be done in amortized O(n) using a hashtable-based set.

Psuedo-code:

s := new HashSet
c := 0
for each el in a
  Add el to s.
    If el was not already in s, move (copy) el c positions left.
    If it was in s, increment c.