leetcode961-- N-Repeated Element in Size 2N Array.

leetcode961-- N-Repeated Element in Size 2N Array.

题目

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


这个题目容易的多,因为除了那个元素之外,其它的元素都只是出现一次,所以只要次数大于1就是它了。

class Solution(object):
    def repeatedNTimes(self, A):
        """
        :type A: List[int]
        :rtype: int
        """
        
        #return (sum(A) - sum(set(A)))/(len(A)/2-1)
        
        dic = {}
        for x in A:
            try:
                dic[x] += 1
            except:
                dic[x] = 1
                
            if dic[x] >1:
                return x
        return None

也可以像加注释的那样用数学公式把它算出来.这里N应该大于1.

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