24 Game LeetCode solution in C++

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class Solution {
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 public:
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  double cor = 0.001;
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  void dfs(vector<double> &cards, bool &res) {
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    if (res == true) return;
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    if (cards.size() == 1) {
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      if (abs(cards[0] - 24) < cor) res = true;
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      return;
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    }
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    for (int i = 0; i < cards.size(); i++) {
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      for (int j = 0; j < i; j++) {
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        double p = cards[i], q = cards[j];
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        vector<double> t{p + q, q - p, p - q, p * q};
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        if (p > cor) t.push_back(q / p);
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        if (q > cor) t.push_back(p / q);
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        cards.erase(cards.begin() + i);
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        cards.erase(cards.begin() + j);
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        for (double d : t) {
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          cards.push_back(d);
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          dfs(cards, res);
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          cards.pop_back();
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        }
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        cards.insert(cards.begin() + j, q);
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        cards.insert(cards.begin() + i, p);
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      }
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    }
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  }
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  bool judgePoint24(vector<int> &cards) {
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    bool res = false;
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    vector<double> card(cards.begin(), cards.end());
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    dfs(card, res);
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    return res;
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  }
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};