Intersection of Multiple Arrays LeetCode solution in C++

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class Solution {
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 public:
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  vector<int> intersection(vector<vector<int>> &nums) {
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    int n = nums.size(); // gives the no. of rows
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    map<int, int> mp;    // we don't need unordered_map because we need the
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                         // elements to be in sorted format.
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    vector<int> vec;
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    // traverse through the 2D array and store the frequency of each element
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    for (int row = 0; row < n; row++) {
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      for (int col = 0; col < nums[row].size(); col++) {
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        mp[nums[row][col]]++;
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      }
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    }
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    // In the 2D array, intersection occurs when the elements are present in
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    // every row. So the frequency of the element should match with the no. or
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    // rows in the 2D array.
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    for (auto element : mp)
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      if (element.second == n) vec.push_back(element.first);
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    // return the intersecting elements
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    return vec;
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  }
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};