BZOJ 1043 【bzoj1043】[HAOI2008]下落的圆盘 | 暴力么??

题目:

---

题解:

大概是黄学长的博客

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
#define N 1010
typedef long long ll;
#define pi acos(-1)
using namespace std;
int n,top;
double ans;
double x[N],y[N],r[N];
struct line
{
    double l,r;
}q[N];
    bool operator < (line a,line b)
	{
	    return a.l<b.l;
	}
inline double dis(int a,int b)
{
    return sqrt((x[a]-x[b])*(x[a]-x[b])+(y[a]-y[b])*(y[a]-y[b]));
}
bool conta(int a,int b)
{
    if (r[a]>=r[b]+dis(a,b)) return 1;
    return 0;
}
void inter(int a,int b)
{
    double d,t,st,l;
    d=dis(a,b);
    t=(r[a]*r[a]-r[b]*r[b]+d*d)/(2*d);
    st=atan2((x[a]-x[b]),(y[a]-y[b]));
    l=acos(t/r[a]);
    q[++top]=(line){(st-l),(st+l)};
}
double cal(int x)
{
    for (int i=x+1;i<=n;i++)
	if (conta(i,x)) return 0;
    top=0;
    for (int i=x+1;i<=n;i++)
    {
	if (!conta(x,i) && r[x]+r[i]>=dis(x,i))
	    inter(x,i);
    }
    double tmp=0,now=0;
    for (int i=1;i<=top;i++)
    {
	if (q[i].l<0) q[i].l+=2*pi;
	if (q[i].r<0) q[i].r+=2*pi;
	if (q[i].l>q[i].r)
	{
	    q[++top]=(line){0,q[i].r};
	    q[i].r=2*pi;
	}
    }
    sort(q+1,q+1+top);
    for (int i=1;i<=top;i++)
	if (q[i].l>now)
	{
	    tmp+=q[i].l-now;
	    now=q[i].r;
	}
	else now=max(now,q[i].r);
    tmp+=2*pi-now;
    return r[x]*tmp;
}
int main()
{
    scanf("%d",&n);
    for (int i=1;i<=n;i++)
	scanf("%lf%lf%lf",&r[i],&x[i],&y[i]);
    for (int i=1;i<=n;i++)
	ans+=cal(i);
    printf("%.3f\n",ans);
    return 0;
}