Iterator for Combination LeetCode solution in C++

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class CombinationIterator {
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 public:
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  vector<string> ans;
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  int j = 0;
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  void comb(int i, string &s, int k, string &t) {
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    if (i == s.size()) {
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      if (t.size() == k) ans.push_back(t);
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      return;
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    }
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    //      Pick
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    t.push_back(s[i]);
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    comb(i + 1, s, k, t);
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    t.pop_back();
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    //      NotPick
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    comb(i + 1, s, k, t);
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  }
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  CombinationIterator(string characters, int combinationLength) {
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    sort(characters.begin(), characters.end());
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    string t = "";
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    comb(0, characters, combinationLength, t);
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  }
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  string next() {
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    return ans[j++];
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  }
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  bool hasNext() {
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    if (j == ans.size()) return false;
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    return true;
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  }
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};