961. N-Repeated Element in Size 2N Array -----E

Q:

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

A:

class Solution {
public:
    int repeatedNTimes(vector<int>& A) {
        unordered_set<int> S;
        for(auto v:A){
            if(S.find(v) !=S.end()){
                return v;
            }
            S.insert(v);
        }
        return 0;//never hit
    }
};