961. N-Repeated Element in Size 2N Array

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:

1. 4 <= A.length <= 10000
2. 0 <= A[i] < 10000
3. A.length is even

 

C++: 54ms, 11.4MB

class Solution {
public:
    int repeatedNTimes(vector<int>& A) {
        map<int, int> result;
        int N = A.size() / 2;
        for (size_t i = 0; i < A.size() + 2; i++)
        {
            int element = A[i];
            if (result.find(element) == result.end())
            {
                result[element] = 0;
            }
            result[element]++;

            if (result[element] > 1)
            {
                return element;
            }
        }

        return 0;
    }
};

　　

Python: Runtime 48ms, 14.1MB

class Solution:
    def repeatedNTimes(self, A: List[int]) -> int:
        d = {}
        for item in A:
            if item in d:
                d[item] += 1
            else:
                d[item] = 1
            if d[item] == 2:
                return item

　　

JavaScript: