LU_CSE2019 K. Five Brothers' Kingdom (WA)

#include<bits/stdc++.h>
using namespace std;
#define x first
#define y second
#define pdd pair<double, double>

double sqr(double a) {
    return a*a;
}
double dist(auto a, auto b) {
    double ret = sqr(a.x-b.x) + sqr(a.y-b.y);
    return sqrt(ret);
}
pdd third_point(auto a, auto b, auto p) {
    pdd c;
    //p(x, y) = (x1+x2+x3)/3, (y1+y2+y3)/3
    c.x = p.x*3.0-(a.x+b.x);
    c.y = p.y*3.0-(a.y+b.y);
    return c;
}
double calc(auto a, auto b, auto c) {
    double area = abs((a.x*(b.y-c.y) + b.x*(c.y-a.y) + c.x*(a.y-b.y))/2.0);
    return area*2.0/dist(b, c);
}

int main() {
    ios_base::sync_with_stdio(false);
    int T;
    pdd a, b, c, i, j;
    cin>>T;
    while(T--) {
        cin>>a.x>>a.y>>b.x>>b.y>>c.x>>c.y>>i.x>>i.y>>j.x>>j.y;
        pdd h = third_point(a, c, i);
        pdd f = third_point(b, c, j);
        double height = calc(b, h, f);

        double ac = dist(a, c);
        double bc = dist(b, c);
        double agdc = ac * height;
        double bgec = bc * height;
        cout<<fixed<<setprecision(9)<<abs(agdc - bgec)<<endl;
    }
    return 0;
}