#include <iostream>
#include <algorithm>
#include <vector>
 
int main() {
  std::vector<int> a{6, 10, 14, 20};
  std::vector<int> b{4, 8, 16, 20};
 
  auto a_size = a.size();
 
  a.insert(a.end(), b.begin(), b.end());
 
  // merge point is where `a` and `b` meet: at the end of original `a`.    
  std::inplace_merge(a.begin(), a.begin() + a_size, a.end());
 
  auto last = std::unique(a.begin(), a.end());
  a.erase(last, a.end());
 
  for(auto e: a) {
    std::cout << e << ' ';
  }
  std::cout << '\n';
}

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