Number of Pairs of Interchangeable Rectangles LeetCode solution in C++

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class Solution {
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 public:
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  long long interchangeableRectangles(vector<vector<int>> &rectangles) {
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    int n = rectangles.size();
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    unordered_map<double, int> mp;
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    for (int i = 0; i < n; i++) {
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      double ratio = rectangles[i][0] / (double)rectangles[i][1];
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      mp[ratio]++;
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    }
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    long long count = 0;
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    for (auto i : mp) {
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      long long x = i.second;
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      x = (x * (x - 1)) / 2.0;
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      count += x;
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    }
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    return count;
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  }
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};