Lucky Numbers in a Matrix LeetCode solution in C++

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class Solution {
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 public:
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  vector<int> luckyNumbers(vector<vector<int>> &matrix) {
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    unordered_map<int, vector<int>> m;
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    for (int i = 0; i < matrix.size(); i++) {
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      vector<int> temp = matrix[i];
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      for (int j = 0; j < temp.size(); j++) {
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        m[j].push_back(temp[j]);
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      }
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    }
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    unordered_map<int, int> mp;
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    for (int i = 0; i < matrix.size(); i++) {
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      vector<int> helper = matrix[i];
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      sort(helper.begin(), helper.end());
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      mp[helper[0]]++;
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    }
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    vector<int> result;
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    for (auto i : m) {
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      vector<int> helper = i.second;
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      sort(helper.begin(), helper.end());
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      int a = helper[helper.size() - 1];
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      if (mp.find(a) != mp.end()) {
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        result.push_back(a);
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      }
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    }
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    return result;
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  }
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};