498A - Crazy Town - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

struct point{
    double x,y;
    point(double x=0, double y=0): x(x), y(y){}
    bool leftOf(point A, point B) {return ((B.x - A.x)*(this -> y - A.y) - (B.y - A.y)*(this -> x - A.x)) > 0;}
};

int main(){
    double x1, y1, x2, y2; cin>>x1>>y1>>x2>>y2;
    int n; cin>>n;
    int cnt = 0;
    point house = {x1, y1};
    point fcgm = {x2, y2};
    while(n--){
        double a, b, c; cin>>a>>b>>c;
        if(a == 0){
            if((-c/b - house.y) < 0 && (-c/b - fcgm.y) > 0 || (-c/b - house.y) > 0 && (-c/b - fcgm.y) < 0) cnt++;
        }
        else if(b == 0){
            if((-c/a - house.x) < 0 && (-c/a - fcgm.x) > 0 || (-c/a - house.x) > 0 && (-c/a - fcgm.x) < 0) cnt++;
        }
        else{
            ll dis1 = (a*x1)+(b*y1)+c;
            ll dis2 = (a*x2)+(b*y2)+c;
            if((dis1>0 && dis2<0) || (dis1<0 && dis2>0)) cnt++;
        }
    }
    cout<<cnt<<endl;
}