41 lines
708 B
C++
41 lines
708 B
C++
//G - ¸Ä¸ï´º·ç´µÂúµØ
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//https://vjudge.net/contest/508277#problem/G
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#include<iostream>
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#include<cstdio>
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#include<cmath>
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#include<cstring>
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using namespace std;
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const int N=101;
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double ans;
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int n,j;
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struct dot
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{
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int x,y;//int->double
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} a[N];
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double cross(double x1,double y1,double x2,double y2)
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{
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// printf("(%d,%d)(%d,%d):%d\n",x1,y1,x2,y2,x1*y2-x2*y1) ;
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return x1*y2-x2*y1;
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}
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int main()
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{
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while(1)
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{
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scanf("%d",&n);
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if(n==0) return 0;
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ans=0;
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memset(a,0,sizeof(dot)*(n+1));
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for(int i=1; i<=n; i++)
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{
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scanf("%d%d",&a[i].x,&a[i].y);
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}
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for(int i=1; i<=n; i++)
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{
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j=i%n+1;
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ans+=(cross(a[i].x,a[i].y,a[j].x,a[j].y)/2);
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}
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printf("%.1lf\n",ans);//Presentation Error
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}
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return 0;
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}
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