this article is made byjason-cow.
welcome to reprint.
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題意，求半平面交，並且保證有解
poj2451
給張圖邊界（|x,y|<=1000,題目為1e4）
別問我為什麼tle
我當成多組處理沒有判斷文末符號，加上就！a！啦！
直接上模板
1 #include 2 #include 3 #include 4 #include 5 #include 6 #include 7 #include 8 #include 9 #include 10 #include11using
namespace
std;
12#define sqr(x) ((x)*(x))
13#define rg register
14#define op operator
15#define il inline
16 typedef double
db;17 typedef bool
bl;18
const db pi=acos(-1.0),eps=1e-10;19
structd22
};23
typedef d v;
24 bl operator
25 v operator+(v a,v b)
26 v operator-(v a,v b)
27 v operator*(v a,db n)
28 v operator/(v a,db n)
2930 db ang(db x)
31 db rad(db x)
32 v rotate(v a,db a)
33 db dis(d a,d b)
34 db cross(v a,v b)
3536 db area(d*r,int
n)41
42 db length(d*r,int
n)47
48struct
l52 l(d p,v v):p(p),v(v)
53bool
operator
54};
5556
d intersect(l a,l b)
6061
bool
left(l l,d a)
6465
int hpi(l*l,int n,d*ans)
77if(head1]=intersect(q[tail-1
],q[tail]);78}
79while(head1]))tail--;
80if(tail-head<=1)return0;
81 p[tail]=intersect(q[tail],q[head]);
82for(int i=head;i<=tail;i++)ans[++m]=p[i];
83return
m;84}85
86const
int maxn=2e4+10;87
l l[maxn];d a[maxn];
88int
main()
97 l[++n]=l(lu,v(0,-1
));98 l[++n]=l(ld,v(1,0
));99 l[++n]=l(rd,v(0,1
));100 l[++n]=l(ru,v(-1,0
));101
int m=hpi(l,n,a);
102 printf("
%.1lf\n
",area(a,m));
103}
104return0;
105 }
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