CF1142C U2

题目链接：洛谷 codeforces

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$y>x^2+bx+c$也就是$y-x^2>bx+c$

左边是点，右边是直线.

维护上凸包.

虽然这么简单但就是做不出来。

 #include<cstdio>
 #include<algorithm>
 #define Rint register int
 using namespace std;
 typedef long long LL;
 const int N = ;
 struct Point {
     LL x, y;
     inline Point(LL _x = , LL _y = ): x(_x), y(_y){}
     inline Point operator - (const Point &o) const {return Point(x - o.x, y - o.y);}
     inline LL operator * (const Point &o) const {return x * o.y - y * o.x;}
     inline bool operator < (const Point &o) const {return x < o.x || x == o.x && y > o.y;}
 } p[N], q[N], stk[N];
 int n, m, top;
 int main(){
     scanf("%d", &n);
     for(Rint i = ;i <= n;i ++){
         scanf("%I64d %I64d", &p[i].x, &p[i].y);
         p[i].y -= p[i].x * p[i].x;
     }
     sort(p + , p + n + );
     q[m = ] = p[];
     for(Rint i = ;i <= n;i ++) if(p[i].x != p[i - ].x) q[++ m] = p[i];
     for(Rint i = ;i <= m;i ++){
         while(top >  && (stk[top] - stk[top - ]) * (q[i] - stk[top - ]) >= ) -- top;
         stk[++ top] = q[i];
     }
     printf("%d\n", top - );
 } // nantf tai qiang le!

CF1142C