# 半平面交模板

bzoj 2618

//%std
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
{
int out = 0, fh = 1;
char jp = getchar();
while ((jp > '9' || jp < '0') && jp != '-')
jp = getchar();
if (jp == '-')
fh = -1, jp = getchar();
while (jp >= '0' && jp <= '9')
out = out * 10 + jp - '0', jp = getchar();
return out * fh;
}
void print(int x)
{
if (x >= 10)
print(x / 10);
putchar('0' + x % 10);
}
void write(int x, char c)
{
if (x < 0)
putchar('-'), x = -x;
print(x);
putchar(c);
}
struct v2
{
double x, y;
v2 operator + (const v2 &rhs) const
{
return (v2){x + rhs.x, y + rhs.y};
}
v2 operator - (const v2 &rhs) const
{
return (v2){x - rhs.x, y - rhs.y};
}
double operator * (const v2 &rhs) const
{
return x * rhs.y - y * rhs.x;
}
v2 operator * (const double &lambda) const
{
return (v2){x * lambda, y * lambda};
}
double angle()
{
return atan2(y, x);
}
};
struct Line
{
v2 p, v;
double angle()
{
return v.angle();
}
friend bool operator < (Line a, Line b)
{
if (a.angle() != b.angle())
return a.angle() < b.angle();
return a.v * b.v < 0;
}
};
v2 Inter(Line a, Line b)
{
v2 u = a.p - b.p;
double t = (b.v * u) / (a.v * b.v);
return a.p + a.v * t;
}
bool Onleft(Line L, v2 p)
{
return L.v * (p - L.p) > 0;
}
const int N = 500 + 10;
v2 p[N], poly[N];
Line q[N], L[N];
int n, head = 1, tail = 0;
double Hpi()
{
sort(L + 1, L + 1 + n);
q[++tail] = L[1];
for (int i = 2; i <= n; ++i) if (L[i].angle() != L[i - 1].angle())
{
{
return 0;
if (q[tail].v * q[tail - 1].v == 0)
return 0;
}
while (head < tail && !Onleft(L[i], p[tail - 1]))
--tail;
q[++tail] = L[i];
p[tail - 1] = Inter(q[tail - 1], q[tail]);
}
--tail;
if (tail - head + 1 <= 2)
return 0.0;
double s = 0;
for (int i = head; i <= tail; ++i)
s += p[i] * p[i + 1];
return fabs(s) / 2;
}
int main()
{
for (int i = 1; i <= t; ++i)
{
for (int j = 1; j <= k; ++j)
poly[k + 1] = poly[1];
for (int j = 1; j <= k; ++j)
{
++n;
L[n].p = poly[j];
L[n].v = poly[j + 1] - poly[j];
}
}
printf("%.3lf\n", Hpi());
return 0;
}


posted @ 2019-08-05 14:57  jklover  阅读(200)  评论(0编辑  收藏  举报