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.html
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.数组
Example:函数
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.
Note:post
1 <= paragraph.length <= 1000.1 <= banned.length <= 100.1 <= banned[i].length <= 10.paragraph may have uppercase symbols, and even if it is a proper noun.)paragraph only consists of letters, spaces, or the punctuation symbols !?',;.
这道题给了咱们一个字符串，是一个句子，里面有不少单词，而且还有标点符号，而后又给了咱们一个相似黑名单功能的一个字符串数组，让咱们在返回句子中出现的频率最高的一个单词。要求很是简单明了，那么思路也就简单粗暴一些吧。由于咱们返回的单词不能是黑名单中的，因此咱们对于每个统计的单词确定都须要去黑名单中检查，为了提升效率，咱们能够把黑名单中全部的单词放到一个HashSet中，这样就能够常数级时间内查询了。而后要作的就是处理一下字符串数组，由于字符串中可能有标点符号，因此咱们先过滤一遍字符串，这里咱们使用了系统自带的两个函数isalpha()和tolower()函数，其实本身写也能够，就放到一个子函数处理一下也不难，这里就偷懒了，遍历每一个字符，若是不是字母，就换成空格符号，若是是大写字母，就换成小写的。而后咱们又使用一个C++中的读取字符串流的类，Java中能够直接调用split函数，叼的飞起。但谁让博主执拗的写C++呢，也无所谓啦，习惯就好，这里咱们也是按照空格拆分，将每一个单词读出来，这里要使用一个mx变量，统计当前最大的频率，还须要一个HashMap来创建单词和其出现频率之间的映射。而后咱们看读取出的单词，若是不在黑名单中内，而且映射值加1后大于mx的话，咱们更新mx，而且更新结果res便可，参见代码以下：url
class Solution { public: string mostCommonWord(string paragraph, vector<string>& banned) { unordered_set<string> ban(banned.begin(), banned.end()); unordered_map<string, int> strCnt; int mx = 0; for (auto &c : paragraph) c = isalpha(c) ? tolower(c) : ' '; istringstream iss(paragraph); string t = "", res = ""; while (iss >> t) { if (!ban.count(t) && ++strCnt[t] > mx) { mx = strCnt[t]; res = t; } } return res; } };
参考资料：spa
https://leetcode.com/problems/most-common-word/code
https://leetcode.com/problems/most-common-word/discuss/124286/Clean-6ms-C%2B%2B-solutionhtm