Naming a Company LeetCode solution in C++

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class Solution {
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 public:
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  long long distinctNames(vector<string> &ideas) {
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    unordered_map<char, unordered_set<string>> mp;
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    for (auto u : ideas) mp[u[0]].insert(u.substr(1, u.size() - 1));
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    long long ans = 0;
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    for (int i = 0; i < 26; i++) {
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      for (int j = i + 1; j < 26; j++) {
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        unordered_set<string> s1 = mp[i + 'a'], s2 = mp[j + 'a'];
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        int comm = 0;
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        for (auto u : s1)
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          if (s2.find(u) != s2.end()) comm++;
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        ans += (long long)(s1.size() - comm) * (long long)(s2.size() - comm) * 2;
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      }
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    }
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    return ans;
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  }
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};