题解 | #数组中重复的数字#

step1: 借助collections的模块进行处理 step2: 遍历collections.Counter的结果

import collections
class Solution:
    def duplicate(self , numbers ):
        if not numbers:
            return -1
        # write code here
        result_dict = collections.Counter(numbers)
        # traverse the dict
        for key,val in result_dict.items():
            if val>1:
                return key