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

You might be able to take advantage of the fact that sum(array) = (n-2)*(n-3)/2 + two missing numbers.

Edit: As others have noted, combined with the sum-of-squares, you can use this, I was just a little slow in figuring it out.