问std：：向量差异

EN

  using namespace std; // For brevity, don't do this in your own code...

  vector<int> v1;
  vector<int> v2;

  // ... Populate v1 and v2

  // For the set_symmetric_difference algorithm to work, 
  // the source ranges must be ordered!    
  vector<int> sortedV1(v1);
  vector<int> sortedV2(v2);

  sort(sortedV1.begin(),sortedV1.end());
  sort(sortedV2.begin(),sortedV2.end());

  // Now that we have sorted ranges (i.e., containers), find the differences    
  vector<int> vDifferences;

  set_symmetric_difference(
    sortedV1.begin(),
    sortedV1.end(),
    sortedV2.begin(),
    sortedV2.end(),
    back_inserter(vDifferences));

  // ... do something with the differences

using namespace std; // For brevity, don't do this in your own code...

// The remove_common_items function template removes some and / or all of the
// items that appear in both of the multisets that are passed to it. It uses the
// items in the first multiset as the criteria for the multi-presence test.
template <typename tVal>
void remove_common_items(unordered_multiset<tVal> &ms1, 
                         unordered_multiset<tVal> &ms2)
{
  // Go through the first hash table
  for (auto cims1=ms1.cbegin();cims1!=ms1.cend();)
  {
    // Find the current item in the second hash table
    auto cims2=ms2.find(*cims1);

    // Is it present?
    if (cims2!=ms2.end())
    {
      // If so, remove it from both hash tables
      cims1=ms1.erase(cims1);
      ms2.erase(cims2);
    }
    else // If not
      ++cims1; // Move on to the next item
  }
}

int main()
{
  vector<int> v1;
  vector<int> v2;

  // ... Populate v1 and v2

  // Create two hash tables that contain the values
  // from their respective initial containers    
  unordered_multiset<int> ms1(v1.begin(),v1.end());
  unordered_multiset<int> ms2(v2.begin(),v2.end());

  // Remove common items from both containers based on the smallest
  if (v1.size()<=v2.size)
    remove_common_items(ms1,ms2);
  else
    remove_common_items(ms2,ms1);

  // Create a vector of the union of the remaining items
  vector<int> vDifferences(ms1.begin(),ms1.end());

  vDifferences.insert(vDifferences.end(),ms2.begin(),ms2.end());

  // ... do something with the differences
}