Triangle - POJ 2954（求三角形内的格子点的个数）

#include<iostream>
#include<string.h>
#include<stdio.h>
#include<algorithm>
#include<math.h>
using namespace std;

const int MAXN = 17;
const double EPS = 1e-10;

struct point
{
    int x, y;
}p[MAXN];

int GCD(int m, int n)
{
    if(!m || !n)
        return m+n;
    return GCD(n, m%n);
}

int main()
{
    while(1)
    {
        int ok=0;

        for(int i=0; i<3; i++)
        {
            scanf("%d%d", &p[i].x, &p[i].y);
            if(p[i].x || p[i].y)
                ok = 1;
        }

        if(!ok)break;
        p[3] = p[0];

        int cnt=0, area=0;

        for(int i=0; i<3; i++)
        {
            cnt += GCD(abs(p[i].x-p[i+1].x), abs(p[i].y-p[i+1].y));
            area += p[i].x*p[i+1].y - p[i].y*p[i+1].x;
        }
        if(area < 0)area = -area;

        printf("%d\n", (area-cnt)/2+1);
    }

    return 0;
}