Codeforces Round #284 (Div. 1) A. Crazy Town 计算几何

题面

题意:给你2个点A和B,和n条直线(ax+by+c=0),给n个a,b,c,求A到B至少跨过多少条直线

题解:对于每条直线,看2个点是否在他同侧,异侧答案就+1

#include<bits/stdc++.h>
using namespace std;
double x1,x2,y11,y2,a,b,c,t1,t2; 
int n,ans;
int main()
{
    cin>>x1>>y11;
    cin>>x2>>y2;
    scanf("%d",&n);
    for(int i=0;i<n;i++)
    {
        cin>>a>>b>>c;
        t1=a*x1+b*y11+c;
        t2=a*x2+b*y2+c;
        if (t1*t2<0) ans++;
    }
    cout<<ans<<endl;
}