Number of Valid Words in a Sentence LeetCode solution in C++

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#include <regex>
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class Solution {
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 public:
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  int countValidWords(string sentence) {
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    int count = 0;
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    // Defining the regex pattern
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    regex valid_word("[a-z]*([a-z]-[a-z])?[a-z]*[!,.]?");
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    // splitting the sentence to words
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    stringstream s(sentence);
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    string word;
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    while (getline(s, word, ' ')) {
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      // Checking if the word matches the regex pattern
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      if (word != "" && regex_match(word, valid_word)) {
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        ++count;
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      }
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    }
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    return count;
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  }
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};