Cod sursă (job #553282)

#include <bits/stdc++.h>
#define y first
#define x second
using namespace std;
ifstream in("infasuratoare.in");
ofstream out("infasuratoare.out");
typedef pair <long long,long long> p;
int n;
p a[1000001];
vector <p> s;
bool stanga(p a,p b,p c)
{ return (a.x-b.x)*(c.y-b.y)<(a.y-b.y)*(c.x-b.x);
}
int main()
{ in>>n;
  for(int i=1;i<=n;i++)
    in>>a[i].x>>a[i].y;
  sort(a+1,a+n+1);
  for(int i=1;i<=n;i++)
  { if(s.size()<2)
    { s.push_back(a[i]);
      continue;
    }
    while(s.size()>=2 && !stanga(s[s.size()-2],s[s.size()-1],a[i]))
      s.pop_back();
    s.push_back(a[i]);
  }
  int k=s.size()-1;
  for(int i=n-1;i>=1;i--)
  { if(s.size()<k+2)
    { s.push_back(a[i]);
      continue;
    }
    while(s.size()>=k+2 && !stanga(s[s.size()-2],s[s.size()-1],a[i]))
      s.pop_back();
    s.push_back(a[i]);
  }
  s.pop_back();
  out<<s.size()<<'\n';
  for(auto it:s)
    out<<it.x<<" "<<it.y<<'\n';
  in.close();
  out.close();
  return 0;
}