leetcode961. N-Repeated Element in Size 2N Array

Posted 2021-01-29 seyjs

题目如下：

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

解题思路：送分题。因为题目没有要求不能用额外的内存，所以我的方法是用字典保存每个数字出现的次数，从而找到出现N的数字。

代码如下：

class Solution(object):
    def repeatedNTimes(self, A):
        """
        :type A: List[int]
        :rtype: int
        """
        dic = {}
        res = 0
        for i in A:
            dic[i] = dic.setdefault(i,0) + 1
            if dic[i] == len(A)/2:
                res = i
                break
        return res