poj2954

题目大意：给定三角形的三个顶点，求内部点有多少。。

思路：先叉积求面积，然后用 S=a + b/2 - 1（皮克公式），a为内部点，b为边上点，求出a。。

code：

/*
  State:Accepted
  Time:2013-04-06 16:40:55
*/
#include<iostream>
#include<fstream>
#include<cstring>
#include<cstdlib>
#include<cstdio>
#include<string>
#include<cmath>
#include<algorithm>
using namespace std;
struct oo{ int  x , y; };
oo a, b, c;

int work_x(int x2, int y2, int x1, int y1){
     return   x1*y2 - x2*y1;  
}

int gcd(int a, int b){
    if  (a % b == 0) return b;
    else return gcd(b , a % b);
}

int work_p(const oo a, const oo b){
     int dx = a.x - b.x;
     int dy = a.y - b.y;
     int d;
     if (dx == 0) d = abs(dy);
     else if (dy == 0) d = abs(dx);
          else d = gcd(abs(dx), abs(dy));
     return d;
}
void solve(){
      int squre = abs(work_x(b.x - a.x, b.y - a.y, c.x - a.x, c.y - a.y));
      int tm = work_p(a, b) + work_p(b,c) + work_p(a,c);
      int ans = (squre + 2 - tm) / 2;
      printf("%d\n",ans);
}

int main(){
     freopen("poj2954.in","r",stdin);
     freopen("poj2954.out","w",stdout); 
     while (scanf("%d%d%d%d%d%d",&a.x, &a.y, &b.x, &b.y, &c.x, &c.y) != EOF){
        if (!a.x && !a.y && !b.x && !b.y && !c.x && !c.y) break;
        solve();    
     }
     fclose(stdin); fclose(stdout);
}