使用临时变量存储

class Solution:
    def duplicate(self , numbers ):
        # write code here
        if len(numbers) == 0:
            return  -1
        temp_list = []
        duplicate_str = ""
        for i in numbers:
            if i not in temp_list:
                temp_list.append(i)
            else:
                duplicate_str = i
                break
        return duplicate_str