65 lines
1.2 KiB
C++
65 lines
1.2 KiB
C++
#include <cstdio>
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#include <iostream>
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#include <cstring>
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#include <algorithm>
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#include <cmath>
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using namespace std;
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#define eps 1e-8
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struct node
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{
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int x,y;
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}
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;
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node p[50005];
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node res[50005];
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int cross(node p0,node p1,node p2)
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{
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return (p0.x-p2.x)*(p1.y-p2.y)-(p1.x-p2.x)*(p0.y-p2.y);
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}
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bool cmp(node a,node b)
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{
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if(a.x==b.x)
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return a.y<b.y;
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else
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return a.x<b.x;
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}
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int Graham(int n)
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{
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int len;
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int top=0;
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sort(p,p+n,cmp);
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for(int i=0; i<n; i++)
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{
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while(top>1&&cross(res[top-1],p[i],res[top-2])<=0)
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top--;
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res[top++]=p[i];
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}
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len=top;
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for(int i=n-2; i>=0; i--)
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{
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while(top>len&&cross(res[top-1],p[i],res[top-2])<=0)
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top--;
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res[top++]=p[i];
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}
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if(n>1)
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top--;
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return top;
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}
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int main()
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{
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int n;
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while(cin>>n)
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{
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for(int i=0; i<n; i++)
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cin>>p[i].x>>p[i].y;
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int dian=Graham(n);
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int ans=-22;
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for(int i=0; i<dian; i++)
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for(int j=i+1; j<dian; j++)
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for(int k=j+1; k<dian; k++)
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ans=max(ans,cross(res[j],res[k],res[i]));
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printf("%.2lf\n",0.5*ans);
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}
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return 0;
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}
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