How to remove all instances of a duplicate from a vector<int>

Question

I've been trying to solve an "easy" leetcode question for two hours now where I need to remove every instance of an int that appears more than once then add the non dupes together. I've tried about 10 different ways and I can only get it to go down to one copy of each int. Here is the nicest solution I've written, but given input {1,2,2,3,4} it would return {1,2,3,4} whereas the expected output is {1,3,4}

  sort(nums.begin(), nums.end()); //Sort numerically
  nums.erase(unique(nums.begin(), nums.end()), nums.end()); 
  return (accumulate(nums.begin(), nums.end(), 0)); 

Answer 1

NlogN complexity, you avoid needing to pre-sort:

Godbolt

#include <set>
#include <vector>

int main()
{
    std::vector<int> nums = {1,2,2,3,5};

    std::multiset<int> m (nums.begin(), nums.end());

    std::size_t sum = 0;
    for (const auto& elem : m)
    {
      sum += m.count(elem) == 1 ? elem : 0;
    }
}

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Update: Could use std::unordered_multiset, as we don't need ordering.