BZOJ1132: [POI2008]Tro

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鬼畜的BZOJ。。。换个输出就A？！！！
叉积的前缀和方法

#include<cstdio>#include<iostream>#include<cstring>#include<cmath>#include<algorithm>using namespace std;#define youhua __attribute__((optimize("O2")))struct Point{    int  x,y;  youhua  inline friend  int operator *(Point a,Point b)    {return a.x*b.y-b.x*a.y;}};Point Pl;Point Sort[3001];youhua inline bool cmp(Point a,Point b){return a*b<0;}Point Line[3001];youhua int main(){    int n;    scanf("%d\n",&n);    int i,j,k,tot;    for(i=1;i<=n;i++)scanf("%d%d",&Line[i].x,&Line[i].y);    long long x,y,ans=0;    for(i=1;i<=n;i++)    {        tot=0;        for(j=1;j<=n;j++)            if(i^j&&((Line[i].y<Line[j].y)||(Line[i].y==Line[j].y&&Line[i].x<Line[j].x)))                Sort[++tot].x=Line[j].x-Line[i].x,Sort[tot].y=Line[j].y-Line[i].y;        sort(Sort+1,Sort+1+tot,cmp);        x=0,y=0;        for(j=1;j<=tot;j++)        {          ans+=y*Sort[j].x-x*Sort[j].y;          x+=Sort[j].x;          y+=Sort[j].y;        }    }    printf("%lld.%d\n",ans>>1,ans&1?5:0);    return 0;}

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