leetcode 笔记5 single number

question:

Given an array of integers, every element appears twice except for one. Find that single one.

my first answer(which is wrong, due to Time Limit Exceeded)

 

the correct answer:

我的思路：一开始想到了转成Serise ,再用value_count, 但是显示没有pandas 包, 所以想到了生成一个字典然后计数