961. N-Repeated Element in Size 2N Array

Problem

You are given an integer array nums with the following properties:

• nums.length == 2 * n.

• nums contains n + 1 unique elements.

• Exactly one element of nums is repeated n times.

Return **the element that is repeated *n* times**.

  Example 1:

Input: nums = [1,2,3,3]
Output: 3

Example 2:

Input: nums = [2,1,2,5,3,2]
Output: 2

Example 3:

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

  Constraints:

• 2 <= n <= 5000

• nums.length == 2 * n

• 0 <= nums[i] <= 10^4

• nums contains n + 1 unique elements and one of them is repeated exactly n times.

Solution (Java)

class Solution {
    public int repeatedNTimes(int[] nums) {
        Set<Integer> set = new HashSet<>();
        for (int num : nums) {
            if (!set.add(num)) {
                return num;
            }
        }
        return -1;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).