Triangle Fun UVA

Triangle Fun

 UVA - 11437 

题意：给三角形，求一些三等分点，线段交点，求面积。

简单题~

#include <bits/stdc++.h>
using namespace std;
const int inf = 0x3f3f3f3f;
const double eps = 1e-12;
const double pi = acos(-1.0);

struct Point {
    double x,y;
    Point (double x = 0, double y = 0) : x(x), y(y) {}
};
typedef Point Vector;
Vector operator + (Vector a, Vector b) {
    return Vector (a.x + b.x, a.y + b.y);
}
Vector operator * (Vector a, double s) {
    return Vector (a.x * s, a.y * s);
}
Vector operator / (Vector a, double p) {
    return Vector (a.x / p, a.y / p);
}
Vector operator - (Point a, Point b) {
    return Vector (a.x - b.x, a.y - b.y);
}
bool operator < (Point a, Point b) {
    return a.x < b.x || (a.x == b.x && a.y < b.y);
}
int dcmp (double x) {
    if(fabs(x) < eps) return 0;
    return x < 0 ? -1 : 1;
}
bool operator == (const Point &a, const Point &b) {
    return dcmp(a.x - b.x) == 0 && dcmp(a.y - b.y) == 0;
}
double Angel (Vector a) {
    return atan2(a.y, a.x);
}
double Dot(Vector a, Vector b) {
    return a.x * b.x + a.y * b.y;
}
double Length (Vector a) {
    return sqrt(Dot(a, a));
}
double Angle (Vector a, Vector b) {
    return acos(Dot(a, b) / Length(a) / Length(b));
}
double Cross (Vector a, Vector b) {
    return a.x * b.y - a.y * b.x;
}
//两直线交点
Point GetLineIntersection (Point p, Vector v, Point q, Vector w) {
    Vector u = p - q;
    double t1 = Cross(w, u) / Cross(v, w);
    double t2 = Cross(v, u) / Cross(v, w);
    return p + v * t1;  //  return q + w * t2;
}
//多边形面积
double ConvexPolygonArea(Point *p, int n) {
    double area = 0;
    for(int i = 1; i < n-1; i++) {
        area += Cross(p[i] - p[0], p[i+1] - p[0]);
    }
    return area / 2;
}

Point p[3],ch[3];
int main(){
    int t;
    //freopen("in.txt", "r", stdin);
    scanf("%d", &t);
    while(t--){
        for(int i = 0; i < 3; i++){
            scanf("%lf %lf", &p[i].x, &p[i].y);
        }
        Point d = p[1] + (p[2] - p[1])/3;
        Point e = p[2] + (p[0] - p[2])/3;
        Point f = p[0] + (p[1] - p[0])/3;
        ch[0] = GetLineIntersection(p[0], d-p[0], p[1], e-p[1]);
        ch[1] = GetLineIntersection(p[2], f-p[2], p[1], e-p[1]);
        ch[2] = GetLineIntersection(p[2], f-p[2], p[0], d-p[0]);
        double area = ConvexPolygonArea(ch,3);
        printf("%.0lf
", area);  //这里是四舍五入，如果强制转换是截断，会WA
    }
}