leetcode Most Common Word——就是在考察自己实现split

819. Most Common Word

Given a paragraph and a list of banned words, return the most frequent word that is not in the list of banned words.  It is guaranteed there is at least one word that isn't banned, and that the answer is unique.

Words in the list of banned words are given in lowercase, and free of punctuation.  Words in the paragraph are not case sensitive.  The answer is in lowercase.

Example:

Input: 
paragraph = "Bob hit a ball, the hit BALL flew far after it was hit."
banned = ["hit"]
Output: "ball"
Explanation: 
"hit" occurs 3 times, but it is a banned word.
"ball" occurs twice (and no other word does), so it is the most frequent non-banned word in the paragraph. 
Note that words in the paragraph are not case sensitive,
that punctuation is ignored (even if adjacent to words, such as "ball,"), 
and that "hit" isn't the answer even though it occurs more because it is banned.

class Solution(object):
    def split_word(self, paragraph):
        sep = set("[!?',;.] ")
        ans = []
        pos = 0
        for i,c in enumerate(paragraph):
            if c in sep:
                word = paragraph[pos:i]
                if word:
                    ans.append(word)
                pos = i+1
        word = paragraph[pos:]
        if word:
            ans.append(word)
        return ans

    def mostCommonWord(self, paragraph, banned):
        """
        :type paragraph: str
        :type banned: List[str]
        :rtype: str
        """
        m = {}
        paragraph = paragraph.lower()
        for w in self.split_word(paragraph):            
            if w in banned: continue
            m[w] = m.get(w, 0)+1
        ans = ""
        max_cnt = 0
        for w,c in m.items():
            if c > max_cnt:
                ans = w
                max_cnt = c
        return ans

使用字符串替换也可以实现，就是找到哪些字符应该直接remove掉，然后再分割：

public static String mostCommonWord(String paragraph, String[] banned) {
        String[] splitArr = paragraph.replaceAll("[!?',;.]","").toLowerCase().split(" ");
        HashMap<String, Integer> map = new HashMap<>();
        List<String> bannedList = Arrays.asList(banned);
        for(String str: splitArr) {
            if(!bannedList.contains(str)) {
                map.put(str, map.getOrDefault(str, 0) + 1);
            }
        }

        int currentMax = 0;
        String res = "";
        for(String key: map.keySet()) {
            res = map.get(key) >  currentMax ? key : res;
            currentMax = map.get(key);
        }
        return res;
    }

还有使用内置python的正则表达式：

Python:
Thanks to @sirxudi I change one line from
words = re.sub(r'[^a-zA-Z]', ' ', p).lower().split()
to
words = re.findall(r'\w+', p.lower())

    def mostCommonWord(self, p, banned):
        ban = set(banned)
        words = re.findall(r'\w+', p.lower())
        return collections.Counter(w for w in words if w not in ban).most_common(1)[0][0]