inplace_merge

// inplace_merge example
#include <iostream>     // std::cout
#include <algorithm>    // std::inplace_merge, std::sort, std::copy
#include <vector>       // std::vector
 
int main () {
  int first[] = {5,10,15,20,25};
  int second[] = {50,40,30,20,10};
  std::vector<int> v(10);
  std::vector<int>::iterator it;
 
  std::sort (first,first+5);
  std::sort (second,second+5);
 
  it=std::copy (first, first+5, v.begin());
     std::copy (second,second+5,it);
 
  //std::inplace_merge (v.begin(),v.begin()+5,v.end());
  std::sort(v.begin(),v.end());
  std::cout << "The resulting vector contains:";
  for (it=v.begin(); it!=v.end(); ++it)
    std::cout << ' ' << *it;
  std::cout << '\n';
 
  return 0;
}

std::inplace_merge (v.begin(),v.begin()+5,v.end());