学步园

原题链接

考察数学知识（百度了好久才找到这个数学知识点）：

在平面上作向量AB、AC

AB叉乘AC为正,则是逆时针,为负为顺时针.

记向量AB为(dx1, dy1) = (x2-x1, y2-y1)向量AC为(dx2, dy2) = (x3-x1, y3-y1)

叉积为
|dx1 dy1|
|dx2 dy2|

即:
dx1 * dy2 - dy1 * dx2

附ac代码：

#include <stdio.h>

int main(){
	int x1, y1, x2, y2, x3, y3, x4, y4, x5, y5, t;
	while(scanf("%d%d%d%d%d%d", &x1, &y1, &x2, &y2, &x3, &y3),
			x1 || y1 || x2 || y2 || x3 || y3){
		x4 = x2 - x1;
		y4 = y2 - y1;
		x5 = x3 - x1;
		y5 = y3 - y1;
		t = x4*y5 - y4*x5;
		if(t > 0)printf("0\n");
		else printf("1\n");
	}		
	return 0;
}