https://leetcode.com/problems/most-common-word/submissions/
import re
import collections
class Solution:
def mostCommonWord(self, paragraph: str, banned: List[str]) -> str:
banned = set(banned)
paragraph = re.sub('[^\\w]',' ', paragraph).lower()
paragraph = [word for word in paragraph.split() if word not in banned]
return collections.Counter(paragraph).most_common(1)[0][0]