CF1142C. U2

 1 #include<bits/stdc++.h>
 2 struct Graph
 3 {
 4     struct Vector
 5     {
 6         long long x,y;
 7         Vector(long long _x=0,long long _y=0){x=_x;y=_y;}
 8         inline friend Vector operator - ( const Vector &u,const Vector &v ) { return Vector(u.x-v.x,u.y-v.y); }
 9         inline friend long long operator ^ ( const Vector &u,const Vector &v ) { return u.x*v.y-u.y*v.x; }
10     }st[1000000];int tp;
11     std::vector<Vector> V,E;
12     inline void add ( long long x,long long y ) { V.push_back(Vector(x,y)); }
13     inline long long solve ( void )
14     {
15         std::sort(V.begin(),V.end(),[&](const Vector &u,const Vector &v){return u.x==v.x ? u.y>v.y : u.x>v.x;});
16         E.push_back(V[0]);
17         for ( int i=1;i<(int)V.size();i++ ) if ( V[i].x!=V[i-1].x ) E.push_back(V[i]);
18         for ( auto p:E )
19         {
20             while ( tp>1 and ((p-st[tp-1])^(st[tp]-st[tp-1]))>=0 ) tp--;
21             st[++tp]=p;
22         }
23         return tp-1;
24     }
25 }G;
26 signed main()
27 {
28     int n;scanf("%d",&n);
29     for ( int i=1,x,y;i<=n;i++ ) scanf("%d%d",&x,&y),G.add(x,y-1LL*x*x);
30     return !printf("%lld\n",G.solve());
31 }