这三分有点。。。。。
by ezoixx130 @ 2018-12-19 19:12:55
@[ezoixx130](/space/show?uid=34886) 我知道我三分挫了
by ezoiHY @ 2018-12-20 12:48:45
```cpp
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
const double eps=1e-8;
int n,top,tmp=1;
double ans;
struct node{
double x,y,att;
bool operator < (const node &b) const {
return fabs(att-b.att)<eps?(att>(atan(-1)/2.0)?x<b.x:x>b.x):att<b.att;
}
}s[100001],p[100001];
double cp(node a1,node a2,node b1,node b2){
return (a2.x-a1.x)*(b2.y-b1.y)-(a2.y-a1.y)*(b2.x-b1.x);
}
double dis(node p1,node p2){
return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}
double dis2(double A,double B,double C,double x0,double y0){
// printf("%lf %lf %lf %lf %lf %lf\n",A,B,C,x0,y0,abs((A*x0+B*y0+C)/sqrt(A*A+B*B)));
return abs((A*x0+B*y0+C)/sqrt(A*A+B*B));
}
int main(){
// freopen("data.in","r",stdin);
scanf("%d",&n);
for(int i=1;i<=n;i++){
scanf("%lf%lf",&p[i].x,&p[i].y);
if(p[i].y<p[tmp].y or (p[i].y==p[tmp].y and p[i].x<p[tmp].x)){
tmp=i;
}
}
swap(p[1],p[tmp]);
for(int i=2;i<=n;i++){
p[i].att=atan2(p[i].x-p[1].x,p[i].y-p[1].y);
}
sort(p+2,p+n+1);
// for(int i=1;i<=n;i++){
// printf("%lf %lf\n",p[i].x,p[i].y);
// }
s[++top]=p[1];
for(int i=2;i<=n;i++){
while(top>1 and cp(s[top-1],s[top],s[top],p[i])>0){
top--;
}
s[++top]=p[i];
}
if(top==3){
printf("0");
return 0;
}
for(int i=1;i<=top;i++){
for(int j=i+2;abs(i-j)>=2;j++,j%=top){
j%=top;
if(j==0)j=top;
double k=(s[i].y-s[j].y)/(s[i].x-s[j].x),b=s[i].y-k*s[i].x;
double d=dis(s[i],s[j]);
double cmps=0;
int l,r;
if(i<j){
l=i+1,r=j-1;
while(r-l>2){
int midl=(l*2+r)/3,midr=(l+r*2)/3;
double tmpl=dis2(k,-1,b,s[midl].x,s[midl].y);
double tmpr=dis2(k,-1,b,s[midr].x,s[midr].y);
if(tmpl>tmpr){
r=midr;
}else {
l=midl;
}
}
double a=dis2(k,-1,b,s[l].x,s[l].y);
double bb=dis2(k,-1,b,s[r].x,s[r].y);
double cc=dis2(k,-1,b,s[(r+l)>>1].x,s[(r+l)>>1].y);
cmps+=d*max(a,max(bb,cc));
l=i-1,r=(j+1)%top;
int aa=0;
if(l==0)l=top;
if(r==0)r=top;
// if(!(l==1 or r==1 or l==top or r==top)){
if(r==0)r=top;
r-=l;
aa=l;
l=top;
r=(r+top)%top;
if(r==0)r=top;
// }
while(r-l>2){
int midl=(l*2+r)/3,midr=(l+r*2)/3;
double tmpl=dis2(k,-1,b,s[(midl+aa)%top!=0?(midl+aa)%top:top].x,s[(midl+aa)%top!=0?(midl+aa)%top:top].y);
double tmpr=dis2(k,-1,b,s[(midr+aa)%top!=0?(midr+aa)%top:top].x,s[(midr+aa)%top!=0?(midr+aa)%top:top].y);
if(tmpl>tmpr){
r=midr;
}else {
l=midl;
}
}
int mid=(((l+r)>>1)+aa)%top;
if(mid==0)mid=top;
l=(l+aa)%top!=0?(l+aa)%top:top;
r=(r+aa)%top!=0?(r+aa)%top:top;
a=dis2(k,-1,b,s[l].x,s[l].y);
bb=dis2(k,-1,b,s[r].x,s[r].y);
cc=dis2(k,-1,b,s[mid].x,s[mid].y);
cmps+=d*max(a,max(bb,cc));
}else {
l=i-1,r=j+1;
while(r-l>2){
int midl=(l*2+r)/3,midr=(l+r*2)/3;
double tmpl=dis2(k,-1,b,s[midl].x,s[midl].y);
double tmpr=dis2(k,-1,b,s[midr].x,s[midr].y);
if(tmpl>tmpr){
r=midr;
}else {
l=midl;
}
}
double a=dis2(k,-1,b,s[l].x,s[l].y);
double bb=dis2(k,-1,b,s[r].x,s[r].y);
double cc=dis2(k,-1,b,s[(r+l)>>1].x,s[(r+l)>>1].y);
cmps+=d*max(a,max(bb,cc));
l=(i+1)%top,r=j-1;
int aa=0;
if(l==0)l=top;
if(r==0)r=top;
// if(!(l==1 or r==1 or l==top or r==top)){
if(l==0)l=top;
l-=r;
aa=r;
r=top;
l=(l+top)%top;
if(l==0)l=top;
// }
while(r-l>2){
int midl=(l*2+r)/3,midr=(l+r*2)/3;
double tmpl=dis2(k,-1,b,s[(midl+aa)%top!=0?(midl+aa)%top:top].x,s[(midl+aa)%top!=0?(midl+aa)%top:top].y);
double tmpr=dis2(k,-1,b,s[(midr+aa)%top!=0?(midr+aa)%top:top].x,s[(midr+aa)%top!=0?(midr+aa)%top:top].y);
if(tmpl>tmpr){
r=midr;
}else {
l=midl;
}
}
int mid=(((l+r)>>1)+aa)%top;
if(mid==0)mid=top;
l=(l+aa)%top!=0?(l+aa)%top:top;
r=(r+aa)%top!=0?(r+aa)%top:top;
a=dis2(k,-1,b,s[l].x,s[l].y);
bb=dis2(k,-1,b,s[r].x,s[r].y);
cc=dis2(k,-1,b,s[mid].x,s[mid].y);
cmps+=d*max(a,max(bb,cc));
}
ans=max(ans,cmps);
}
}
// printf("%d\n",top);
printf("%.3lf",ans/2);
return 0;
}
```
by ezoiHY @ 2018-12-20 12:50:25
%旋转卡壳用三分
by zzw4257 @ 2019-01-06 20:27:29