819. Most Common Word

class Solution(object):
    def mostCommonWord(self, paragraph, banned):
        """
        :type paragraph: str
        :type banned: List[str]
        :rtype: str
        """
        res=''
        cnt={res:0}
        for word in paragraph.split():
            word=word.lower().strip("!?',;.")
            if word not in banned:
                if word not in cnt:
                    cnt[word]=1
                else:
                    cnt[word]+=1
                if cnt[word]>cnt[res]:
                    res=word
        return res

class Solution(object):
    def mostCommonWord(self, paragraph, banned):
        banset = set(banned)
        count = collections.Counter(
            word.strip("!?',;.") for word in paragraph.lower().split())

        ans, best = '', 0
        for word in count:
            if count[word] > best and word not in banset:
                ans, best = word, count[word]

        return ans