Как ускорить логику цикла? [for experts]

#include <iostream>
#include <sstream>
#include <map>
 
using namespace std;
 
void scanSeq(istream & is, ostream & os)
{
    map<int, int> intervs;
    size_t L, N;
    int from, to;
    is>>L;
    is>>N;
    
    for (size_t i = 0; i<N; ++i)
    {
        is>>from>>to;
        intervs[from]=to;
    }
 
    int pos_b = 0, pos_e;
    for (auto i : intervs)
    {
        pos_e = i.first;
        if (pos_e>pos_b)
           os<<pos_b<<" "<<pos_e<<endl;
        pos_b = i.second;
    }
    if (pos_b < L)
        os<<pos_b<<" "<<L<<endl;
}
int main()
{
    stringstream ss;
    ss<<10<<endl<<3<<endl<<"5 6"<<endl<<"1 2"<<endl<<"7 9";
    scanSeq(ss, cout);
}

class Line
{
public:
    bool operator<(const Line&line)const{return x<line.x;}
 
    int x,y;
};
 
int main()
{
    std::size_t lenght,lineListSize;
    std::cin>>lenght>>lineListSize;
    std::vector<Line> lineList;
    for(std::size_t i=0;i<lineListSize;++i)
    {
        int x,y;
        std::cin>>x>>y;
        lineList.push_back({x,y});
    }
    std::sort(lineList.begin(),lineList.end());
    auto writePos=lineList.begin();
    for(auto readPos=lineList.begin()+1;readPos<lineList.end();++readPos)
    {
        if(writePos->x<=readPos->x && readPos->x<=writePos->y)
            writePos->y=std::max(writePos->y,readPos->y);
        else
            *++writePos=*readPos;
    }
    lineList.erase(++writePos,lineList.end());
    std::cout<<"{0,"<<lineList.front().x<<"} ";
    for(auto line=lineList.begin();line+1<lineList.end();++line)
        std::cout<<"{"<<line[0].y<<" "<<line[1].x<<"} ";
    std::cout<<"{"<<lineList.back().y<<","<<lenght<<"}";
    return 0;
}

#include <vector>
#include <algorithm>
#include <iostream>
 
int main()
{
  int length = 0;
  std::cin >> length;
 
  unsigned n_segments = 0;
  std::cin >> n_segments;
 
  std::vector<std::pair<int, int>> points; 
 
  for (unsigned i = 0; i < n_segments; ++i)
  {
    int xl = 0, xr = 0;
    std::cin >> xl >> xr;
    points.emplace_back(xl, +1);
    points.emplace_back(xr, -1);
  }
 
  points.emplace_back(length, +1);
 
  std::sort(points.begin(), points.end());
 
  int n_coverage = 0;
  int prev_x = 0;
 
  for (const auto &point : points)
  {
    if (n_coverage == 0 && prev_x != point.first)
      std::cout << prev_x << " " << point.first << std::endl;
 
    prev_x = point.first;
    n_coverage += point.second;
  }
}