Count Words Obtained After Adding a Letter LeetCode solution in C++

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class Solution {
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 public:
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  int wordCount(vector<string> &startWords, vector<string> &targetWords) {
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    set<vector<int>> hash;
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    for (int i = 0; i < startWords.size(); i++) {
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      vector<int> counter(26, 0);
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      for (char &x : startWords[i]) {
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        counter[x - 'a']++;
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      }
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      hash.insert(counter);
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    }
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    int ans = 0;
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    for (int i = 0; i < targetWords.size(); i++) {
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      vector<int> counter(26, 0);
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      for (char &x : targetWords[i]) {
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        counter[x - 'a']++;
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      }
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      for (int j = 0; j < 26; j++) {
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        if (counter[j] == 1) {
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          counter[j] = 0;
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          if (hash.find(counter) != hash.end()) {
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            ans++;
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            break;
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          }
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          counter[j] = 1;
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        }
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      }
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    }
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    return ans;
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  }
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};