Q961 N-Repeated Element in Size 2N Array

N-Repeated Element in Size 2N Array

Question

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

Approach 1: Hash Table (Original Answer)

Intuition and Algorithm

Using Hash table to distinguish repeated element in array A.

class Solution:
    def repeatedNTimes(self, A):
        Hashmap=dict()
        # 建立Hash Table
        for i in range(0, len(A)):
            if not(A[i] in Hashmap):
                Hashmap[A[i]] = i #键是数值，值是序号
            else:
                return A[i]

def main():
    A =[5,1,5,2,5,3,5,4]
    answer=Solution()
    results=answer.repeatedNTimes(A)
    print(results)


if __name__ == "__main__":
    main()

• Runtime: 48 ms, faster than 85.41% of Python3 online submissions for N-Repeated Element in Size 2N Array.
• Memory Usage: 14.1 MB, less than 5.12% of Python3 online submissions for N-Repeated Element in Size 2N Array.