2 2 2 -0.5 0 0.5 0 3 3 0 1 1 0 -1 0
Case #1: 0.3183 Case #2: 0.5123
#include <cstdio>
#include <cstdlib>
#include <cmath>
#define N 200
#define inf 1e-6
#define PI 3.141592653
typedef struct
{
double x;
double y;
}point;
point points[N];
point chs[N];
int sp;
//求凸包周长的模板
double dis(point a, point b)
{
return sqrt((a.x - b.x) * (a.x - b.x) * 1.0 + (a.y - b.y) * (a.y - b.y));
}
double multi(point p0, point p1, point p2)
{
return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);
}
int cmp(const void *p, const void *q)
{
point a = *(point *)p;
point b = *(point *)q;
double k = multi(points[0], a, b);
if(k < -inf)
return 1;
else if(fabs(k) < inf && (dis(a, points[0]) - dis(b, points[0])) > inf)
return 1;
else return -1;
}
void convex_hull(int n)
{
int k, d;
double miny = points[0].y;
int index = 0;
for(int i = 1; i < n; i++)
{
if(points[i].y < miny)
{
miny = points[i].y;
index = i;
}
else if(points[i].y == miny && points[i].x < points[index].x)
index = i;
}
point temp;
temp = points[index];
points[index] = points[0];
points[0] = temp;
qsort(points+1, n-1, sizeof(points[0]), cmp);
chs[0] = points[n-1];
chs[1] = points[0];
sp = 1;
k = 1;
while(k <= n-1)
{
double d = multi(chs[sp], chs[sp-1], points[k]);
if(d <= 0)
{
sp++;
chs[sp] = points[k];
k++;
}
else sp--;
}
}
int main()
{
double sum, d;
int T, n;
scanf("%d",&T);
for(int Ca = 1; Ca <= T; Ca++)
{
sum = 0;
scanf("%d %lf", &n, &d);
if(n == 0 || n == 1)
{
printf("Case #%d: 0.0000\n", Ca);
continue;
}
for(int i = 0; i < n; i++)
scanf("%lf%lf", &points[i].x, &points[i].y);
if(n == 2)
{
double len = dis(points[0],points[1]);
printf("Case #%d: %.4f\n", Ca, (2 * len) / (PI * d));
continue;
}
convex_hull(n);
for(int i = 1; i <= sp; i++)
sum += dis(chs[i-1], chs[i]);
sum += dis(chs[0], chs[sp]); //算出凸包周长
printf("Case #%d: %.4f\n", Ca, sum / (PI * d));
}
}
HDU 4978 A simple probability problem,布布扣,bubuko.com
HDU 4978 A simple probability problem
原文地址：http://blog.csdn.net/tc_to_top/article/details/38705757
