poj 1654 Area

求多边形的面积；

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#include<iostream>

#include<cstdio>

#include<cstdlib>

#include<algorithm>

#include<cmath>

#include<queue>

#include<set>

#include<map>

#include<cstring>

#include<vector>

using namespace std;

class Point

{

public:

      int x,y;    

}point[1000024],d[10];



Point Get_point( Point a, int num )

{

    Point b;

    b.x = a.x + d[num].x;

    b.y = a.y + d[num].y;

    return b;    

}

int multi( Point p1, Point p2 , Point q )

{

   return ( p1.x - q.x )*( p2.y - q.y ) - ( p2.x - q.x )*( p1.y - q.y );

}

void Initial( )

{

    d[1].x = -1; d[1].y = -1;

    d[2].x = 0 ; d[2].y = -1;

    d[3].x = 1 ; d[3].y = -1;

    d[4].x = -1; d[4].y = 0;

    d[6].x = 1 ; d[6].y = 0;

    d[7].x = -1; d[7].y = 1;

    d[8].x = 0 ; d[8].y = 1;

    d[9].x = 1 ; d[9].y = 1;    

};

int main(  )

{

   int n;

   Initial();

   char str[1000024];

   while( scanf( "%d",&n )==1 )

   {

      while( n-- )

      {

          int i = 1;

          scanf( "%s",str + 1 );

          point[0].x = 0 ; point[1].y = 0;

          while( str[i]!='5' )

          {

             point[i] = Get_point( point[i-1] , str[i]-'0' );    

             i++;

          }    

          double ans = 0;

          for( int j = 1 ; j < i -1 ; j++ )

          {

               ans += multi( point[j] ,point[j+1],point[0]);    

          }

          ans = fabs( ans/2 );

          if( fabs(ans - ( long long  )ans) < 1.0e-8  )    

          printf( "%.0f\n",ans );

          else printf( "%.1f\n",ans );

      }        

   }

    //system( "pause" );

    return 0;

}