Problem Address：http://acm.zjut.edu.cn/ShowProblem.aspx?ShowID=1051
简单题。
捡了一个公式：
S△=1/2 * |(x2-x1)(y3-y1)-(x3-x1)(y2-y1)|
贴代码：
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
int x1,y1,x2,y2,x3,y3;
scanf("%d %d %d %d", &x1, &y1, &x2, &y2);
double d2=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
double d=0.0,h;
while(scanf("%d %d", &x3, &y3)!=EOF)
{
h = (x2-x1)*(y3-y1)-(x3-x1)*(y2-y1);
if (h<0) h = -h;
h = double(h)/ (double)d2;
if (h>d) d=h;
}
printf("%.3f/n", d);
return 0;
}