Find All Lonely Numbers in the Array LeetCode solution in C++

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class Solution {
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 public:
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  vector<int> findLonely(vector<int> &nums) {
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    int n = nums.size();
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    unordered_map<int, int> ump;
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    vector<int> sol;
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    for (int i = 0; i < n; i++) {
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      ump[nums[i]]++;
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    }
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    for (auto a : ump) {
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      if (a.second == 1 and !ump.count(a.first + 1) and !ump.count(a.first - 1))
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        sol.push_back(a.first);
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    }
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    return sol;
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  }
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};