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

Description

https://leetcode.com/problems/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:

  • 4 <= A.length <= 10000
  • 0 <= A[i] < 10000
  • A.length is even

Explanation

Count the element occurrences and find the element occurs N times.

Python Solution

class Solution:
    def repeatedNTimes(self, A: List[int]) -> int:
        n = len(A) // 2
        
        counter = {}
        
        for num in A:
            counter[num] = counter.get(num, 0) + 1
            
            
        for key, value in counter.items():            
            if value == n:
                return key
            
        return -1
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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