POJ 2954-Triangle(计算几何+皮克定理)

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>
#include <iostream>
#include <sstream>
#include <algorithm>
#include <set>
#include <queue>
#include <stack>
#include <map>
using namespace std;
typedef long long LL;
const int inf=0x3f3f3f3f;
const double pi= acos(-1.0);
const double esp=1e-6;
int gcd(int a,int b)
{
while(b){
int r=b;
b=a%b;
a=r;
}
return a;
}
int main()
{
int x1,y1,x2,y2,x3,y3;
double S;
int in,on;
while(~scanf("%d %d %d %d %d %d",&x1,&y1,&x2,&y2,&x3,&y3)){
in=on=S=0;
if(!x1&&!y1&&!x2&&!y2&&!x3&&!y3) break;
S=(x2-x1)*(y3-y1)-(x3-x1)*(y2-y1);
if(S<0)
S=-S;
on=gcd(abs(x2-x1),abs(y2-y1))+gcd(abs(x1-x3),abs(y1-y3))+gcd(abs(x3-x2),abs(y3-y2));
in=(S+2-on)/2;
printf("%d\n",in);
}
return 0;
}