Finding Duplicates in Array and printing them only Once

Question

I am trying to loop through my array and find all the numbers that are repeating more than once:

E.G: if there is 1 1 2 3 4

It should print saying \

Answer 1

Just add the number you will find duplicated to some structure like HashSet or HashMap so you can find it later when you will detect another duplication.

Set printed = new HashSet();

  for(int i=0; i

Better O(n) alghorithm:

Set printed = new HashSet();

  for(int i=0; i