Count Common Words With One Occurrence LeetCode solution in C++

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class Solution {
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 public:
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  int countWords(vector<string> &words1, vector<string> &words2) {
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    unordered_map<string, int> freq1, freq2;
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    for (auto &s : words1) ++freq1[s];
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    for (auto &s : words2) ++freq2[s];
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    int ans = 0;
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    for (auto &[s, v] : freq1)
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      if (v == 1 && freq2[s] == 1) ++ans;
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    return ans;
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  }
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};