Equal Row and Column Pairs LeetCode solution in C++

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class Solution {
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 public:
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  int equalPairs(vector<vector<int>> &grid) {
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    // Number to store the count of equal pairs.
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    int ans = 0;
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    map<vector<int>, int> mp;
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    // Storing each row int he map
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    for (int i = 0; i < grid.size(); i++) mp[grid[i]]++;
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    for (int i = 0; i < grid[0].size(); i++) {
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      vector<int> v;
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      // extracting column in a vector.
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      for (int j = 0; j < grid.size(); j++) v.push_back(grid[j][i]);
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      // Add the number of times that column appeared as a row.
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      ans += mp[v];
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    }
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    // Return the number of count
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    return ans;
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  }
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};