poj 2451 半平面交 板子

poj 2451

半平面，一條直線可以把平面分成兩部分，即稱為半平面

半平面交，即多條直線劃分出的相交的平面的面積

學習大佬的**，清晰易懂，打算當成以後的模板用了

**(基於poj 2451)：

#include #include #include #include #include using namespace std;

const double eps = 1e-8;
int n, pn, dq[20005], top, bot;
struct point p[20005];
struct line 
} l[20005];
int dblcmp(double k) 
double multi(point p0, point p1, point p2) 
bool cmp(const line& l1, const line& l2) 
void addline(line& l, double x1, double y1, double x2, double y2) 
void getintersect(line l1, line l2, point& p) 
bool judge(line l0, line l1, line l2) 
void halfplaneintersect( ) 
while (top > bot && judge(l[dq[bot]], l[dq[top]], l[dq[top-1]])) top--;
while (top > bot && judge(l[dq[top]], l[dq[bot]], l[dq[bot+1]])) bot++;
dq[++top] = dq[bot]; 
for (pn = 0, i = bot; i < top; i++, pn++)
getintersect(l[dq[i+1]], l[dq[i]], p[pn]);
}double getarea() 
int main()
addline(l[n++], 0, 0, 10000, 0);
addline(l[n++], 10000, 0, 10000, 10000);
addline(l[n++], 10000, 10000, 0, 10000);
addline(l[n++], 0, 10000, 0, 0);
halfplaneintersect();
printf ("%.1lf\n", getarea());
}return 0;
}

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