Codility - Distinct (JavaScript)

Lesson 6 - Sorting

Task Description:
Write a function
class Solution { public int solution(int[] A); }
that, given an array A consisting of N integers, returns the number of distinct values in array A.

For example, given array A consisting of six elements such that:
A[0] = 2 A[1] = 1 A[2] = 1
A[3] = 2 A[4] = 3 A[5] = 1

the function should return 3, because there are 3 distinct values appearing in array A, namely 1, 2 and 3.

Write an efficient algorithm for the following assumptions:
N is an integer within the range [0..100,000];
each element of array A is an integer within the range [−1,000,000..1,000,000].

[kylebarvel]

I used a Set object and return its size

[ctchan]

I also solve it by hash table, it doesn't need sorting algorithm, but it's in sorting lesson. Confused !