1 #include<stdio.h>
2 #include<math.h>
3 typedef struct dian
4 {
5 int x,y;
6 };
7 dian p[50005],ch[50005];
8 double area(int i,int j,int k)
9 {
10 double a,b,c,q;
11 a=sqrt(1.0*(ch[j].x-ch[i].x)*(ch[j].x-ch[i].x)+1.0*(ch[j].y-ch[i].y)*(ch[j].y-ch[i].y));
12 b=sqrt(1.0*(ch[k].x-ch[i].x)*(ch[k].x-ch[i].x)+1.0*(ch[k].y-ch[i].y)*(ch[k].y-ch[i].y));
13 c=sqrt(1.0*(ch[j].x-ch[k].x)*(ch[j].x-ch[k].x)+1.0*(ch[j].y-ch[k].y)*(ch[j].y-ch[k].y));
14 q=(a+b+c)/2;
15 return(sqrt(q*(q-a)*(q-b)*(q-c)));
16 }
17 int cross(dian p1,dian p2,dian p3)
18 {
19 int x1=p2.x-p1.x,y1=p2.y-p1.y;
20 int x2=p3.x-p1.x,y2=p3.y-p1.y;
21 return(x1*y2-x2*y1);
22 }
23 void sort(int l,int r)
24 {
25 int i,j,x,x1,y;
26 i=l; j=r;
27 x=p[(i+j)/2].x; x1=p[(i+j)/2].y;
28 while (i<=j)
29 {
30 while (p[i].x<x||(p[i].x==x&&p[i].y<x1)) i++;
31 while (x<p[j].x||(p[j].x==x&&x1<p[j].y)) j--;
32 if (i<=j){
33 y=p[i].x; p[i].x=p[j].x; p[j].x=y;
34 y=p[i].y; p[i].y=p[j].y; p[j].y=y;
35 i++; j--;
36 }
37 }
38 if (i<r) sort(i,r);
39 if (l<j) sort(l,j);
40 }
41 int main()
42 {
43 int n,i,sum,j,k;
44 double max;
45 while (~scanf("%d",&n)&&n!=-1)
46 {
47 for (i=1;i<=n;i++) scanf("%d%d",&p[i].x,&p[i].y);
48
49 sort(1,n);
50 sum=1;
51 for (i=1;i<=n;i++){
52 while (sum>=3&&cross(ch[sum-2],ch[sum-1],p[i])<=0) sum--;
53 ch[sum]=p[i];
54 sum++;
55 }
56 k=sum-1;
57 for (i=n-1;i>=1;i--){
58 while (sum>=k+2&&cross(ch[sum-2],ch[sum-1],p[i])<=0) sum--;
59 ch[sum]=p[i];
60 sum++;
61 }
62 sum--;
63 // for (i=1;i<=sum;i++) printf("%d %d\n",ch[i].x,ch[i].y);
64 max=0.00;
65
66 // j=2; k=3;
67 ch[sum+1]=ch[2];
68 for (i=1;i<=sum-2;i++)
69 {
70 j=i+1; k=j+1;
71 while (area(i,j,k)<area(i,j,k+1)) {k++; if (k>sum) k=1; }
72 if (area(i,j,k)>max) max=area(i,j,k);
73 while (area(i,j,k)<area(i,j+1,k)) {j++; if (j>sum) j=1; }
74 if (area(i,j,k)>max) max=area(i,j,k);
81 }
82 printf("%.2lf\n",max);
83 }
84 }
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