Mean of Array After Removing Some Elements LeetCode solution in C++

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class Solution {
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 public:
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  double trimMean(vector<int> &arr) {
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    auto first = arr.begin() + arr.size() / 20;
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    auto second = arr.end() - arr.size() / 20;
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    nth_element(arr.begin(), first, arr.end());
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    nth_element(first, second, arr.end());
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    return accumulate(first, second, 0.0) / distance(first, second);
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  }
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};