N-Repeated Element in Size 2N Array - Hash Table - Easy - LeetCode

In an array A of size 2N, there are N+1 unique elements, and exactly one of these elements is repeated N times.

Return the element repeated N times.

Example 1:

Input: [1,2,3,3] Output: 3 Example 2:

Input: [2,1,2,5,3,2] Output: 2 Example 3:

Input: [5,1,5,2,5,3,5,4] Output: 5

Note:

4 <= A.length <= 10000 0 <= A[i] < 10000 A.length is even

public class Solution {
 public int RepeatedNTimes(int[] A) {
 var set = new HashSet<int>();
 for(int i=0;i<A.Length;i++){
 if(set.Contains(A[i])){
 return A[i];
 }
 set.Add(A[i]);
 }
 return -1;
 }
}

Time Complexity: O(n)

Space Complexity: O(n)