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## 为什么我area/4才对？？？？？？？？

Posted by jinhouyu at 2015-07-25 11:20:55 on Problem 1654
#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<algorithm>
#include<iostream>
#define INF 0x7fffffff
#define eps 1e-8
#define manx 1000005
typedef long long LL;
using namespace std;

char step[manx];
double xo,yo;
struct Point{
double x,y;
};
double Multi(Point p1,Point p2)
{
return (p2.x*p1.y)-(p1.x*p2.y);
}
void Move(char ch)
{
switch(ch)
{
case '8':{yo+=1;break;}
case '2':{yo-=1;break;}
case '6':{xo+=1;break;}
case '4':{xo-=1;break;}
case '9':{xo+=1;yo+=1;break;}
case '7':{xo-=1;yo+=1;break;}
case '3':{xo+=1;yo-=1;break;}
case '1':{xo-=1;yo-=1;break;}
case '5':{xo=0;yo=0;break;}
}
}
int main()
{
int T,i;
char ch1,ch2;
scanf("%d",&T);
getchar();
while(T--)
{
double sum=0.0;
xo=0.0,yo=0.0;
gets(step);
for(i=0;step[i]!='5';i++)
{
Point a,b;
Move(step[i]);
a.x=xo;
a.y=yo;
Move(step[i+1]);
b.x=xo;
b.y=yo;
if(step[i+1]=='5')
break;
sum+=Multi(a,b);
}
sum=fabs(sum)/4;//求解为什么。。。。。
if(sum-floor(sum)<eps)
printf("%.f\n",sum);
else
printf("%.1f\n",sum);
}
return 0;
}

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