Card Flipping Game LeetCode solution in C++

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class Solution {
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 public:
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  int flipgame(vector<int> &fronts, vector<int> &backs) {
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    int n = fronts.size();
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    map<int, int> mp;
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    set<int> s;
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    for (int i = 0; i < n; i++) {
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      if (fronts[i] == backs[i]) {
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        mp[fronts[i]]++;
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      }
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      s.insert(fronts[i]);
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      s.insert(backs[i]);
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    }
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    for (auto i : s) {
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      if (mp[i] >= 1) continue;
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      return i;
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    }
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    return 0;
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  }
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};