pku 1654[计算几何]

pku 1654[计算几何]

500MS弄到79MS，求多边形面积，有可能是凹，用叉积就可以了，不能存所有点，会MLE
一次读入比单个读入快

#include < iostream >
#include < math.h >
using   namespace  std;
struct  point  {__int64 x,y;} ;
__int64 dx[] = {0,-1,0,1,-1,0,1,-1,0,1} ;
__int64 dy[] = {0,-1,-1,-1,0,0,0,1,1,1} ;

// __int64 xmult(point p0,point p1,point p2){
//     return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
// }
char  path[ 1000010 ];
int  main()
{
    int t;
    point p0,p1,p2;
    __int64 ans;
    scanf("%d",&t);
    while(t--)
    {
        p0.x=0;
        p0.y=0;
        p2=p1=p0;
        ans=0;
        scanf(" %s",path);
        int i=0;
        for(i=0;path[i]!='5';i++)
        {
            p1=p2;
            p2.x+=dx[path[i]-'0'];
            p2.y+=dy[path[i]-'0'];
            ans+=(p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
        }
        if(ans<0) ans*=-1;
        printf("%I64d",(ans>>1));
        if(((ans>>1)<<1)==ans) printf("\n"); 
        else printf(".5\n");
    }
    return 0;
}