Problem

In a 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

Pre analysis

Given the conditions, will check whether a occurence had already been present before.

Another Solution

1. Use of Set as Data Structure with above same logic

   var repeatedNTimes = function(A) {
       const numSet = new Set();
       for (let a of A) {
           if (numSet.has(a)) return a;
               numSet.add(a);
           }
       return null;
   };