Check If N and Its Double Exist LeetCode solution in C++

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class Solution {
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 public:
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  bool checkIfExist(vector<int> &arr) {
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    sort(arr.begin(), arr.end());
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    int i = 0;
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    int j = 1;
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    int n = arr.size();
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    while (i < n && j < n) {
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      if (arr[i] < 0 && arr[j] < 0 && arr[i] == 2 * arr[j])
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        return true;
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      else if (2 * arr[i] < arr[j]) {
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        i++;
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      } else if (2 * arr[i] > arr[j])
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        j++;
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      else if (i == j && arr[i] == 0) {
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        i++;
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        j++;
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      }
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      else
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        return true;
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    }
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    return false;
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  }
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};