# 慢
words_dic = {}
for word in words:
if word in words_dic.key():
words_dic[word] += 1
else:
words_dic[word] = 1
# 快
words_dic = {}
for word in words:
if word in words_dic:
words_dic[word] += 1
else:
words_dic[word] = 1刷 leetcode 的时候发现自己提交的代码总是比示例代码要多200ms，最后发现把 .keys() 删掉就可以了！！！
