Algorithm to find two repeated numbers in an array, without sorting

Question

There is an array of size n (numbers are between 0 and n - 3) and only 2 numbers are repeated. Elements are placed randomly in the array.

E.g. in {2, 3, 6, 1, 5, 4

Answer 1

Without sorting you're going to have a keep track of numbers you've already visited.

in psuedocode this would basically be (done this way so I'm not just giving you the answer):

for each number in the list
   if number not already in unique numbers list
      add it to the unique numbers list
   else
      return that number as it is a duplicate
   end if
end for each