Solution to Leetcode problem 961 N-Repeated Element in Size 2N Array

This is the first problem of Leetcode contest 116. This is easy enough and I left below my solution in Java.

Leetcode problem statement and stats

Given an array A of size 2N, containing N+1 distinct elements with one element appearing N times exactly. Return that element.

One could simply follow the question and count the number of times each element occurs in A in a Map<Integer, Integer>, but you could also notice that all the other N elements must appear only once. Therefore the question becomes which element appears at least twice in the array. To answer this question, you only need to iterate through A remembering all previous elements encountered (in a Set for instance). This is what I have done in the solution below.

class Solution {
    public int repeatedNTimes(int[] A) {
        Set<Integer> seenNumbers = new HashSet<>();
        for (int num : A) {
            if (seenNumbers.contains(num)) {
                return num;
            }
            seenNumbers.add(num);
        }
        // Should not be reached
        return 0;
    }
}