Codility - Distinct

Write a function

function solution(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].
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1. 주어진 배열에서 중복을 제거한 배열을 만든 후 그 크기값을 return 한다.

function solution(A) {
    // write your code in JavaScript (Node.js 8.9.4)
    return [...new Set(A)].length;
}