UVa 11437 Triangle Fun(几何)

题目链接：UVa 11437  Triangle Fun

几何，用向量可以做。

#include <iostream>#include <cstdio>#include <cmath>using namespace std;const double eps = 1e-10;struct Point{double x, y;Point(double x=0, double y=0):x(x),y(y) { }};typedef Point Vector;Vector operator + (const Vector& A, const Vector& B){    return Vector(A.x+B.x, A.y+B.y);}Vector operator - (const Point& A, const Point& B){    return Vector(A.x-B.x, A.y-B.y);}Vector operator * (const Vector& A, double p){    return Vector(A.x*p, A.y*p);}bool operator < (const Point& a, const 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;    else        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 Dot(const Vector& A, const Vector& B){    return A.x*B.x + A.y*B.y;}double Length(const Vector& A){    return sqrt(Dot(A, A));}double Angle(const Vector& A, const Vector& B){    return acos(Dot(A, B) / Length(A) / Length(B));}double Cross(const Vector& A, const Vector& B){    return A.x*B.y - A.y*B.x;}double Area2(Point A, Point B, Point C){    return Cross(B - A, C - A);}bool SegmentProperIntersection(const Point& a1, const Point& a2, const Point& b1, const Point& b2){double c1 = Cross(a2-a1,b1-a1), c2 = Cross(a2-a1,b2-a1),c3 = Cross(b2-b1,a1-b1), c4=Cross(b2-b1,a2-b1);return dcmp(c1)*dcmp(c2)<0 && dcmp(c3)*dcmp(c4)<0;}bool OnSegment(const Point& p, const Point& a1, const Point& a2){return dcmp(Cross(a1-p, a2-p)) == 0 && dcmp(Dot(a1-p, a2-p)) < 0;}//求两直线交点，先确保两直线有唯一交点，当且仅当Cross(v, w)非0Point GetLineIntersection(const Point& P, const Point& v, const Point& Q, const Point& w){Vector u = P-Q;double t = Cross(w, u) / Cross(v, w);return P+v*t;}Vector Rotate(const Vector& A, double rad){return Vector(A.x*cos(rad)-A.y*sin(rad), A.x*sin(rad)+A.y*cos(rad));}double DistanceToLine(Point P, Point A, Point B){    Vector v1 = B - A, v2 = P - A;    return fabs(Cross(v1, v2)) / Length(v1); // 如果不取绝对值，得到的是有向距离}int main(){    int T, n;    Point a, b, c, d, f, e, r, p, q;    scanf("%d", &T);    while(T--)    {        scanf("%lf%lf", &a.x, &a.y);        scanf("%lf%lf", &b.x, &b.y);        scanf("%lf%lf", &c.x, &c.y);        d = b + (c - b) * (1.0 / 3.0);        f = a + (b - a) * (1.0 / 3.0);        e = c + (a - c) * (1.0 / 3.0);        r = GetLineIntersection(a, a - d, c, c - f);        p = GetLineIntersection(a, a - d, b, b - e);        q = GetLineIntersection(b, b - e, c, c - f);        int res = (int)(fabs(Area2(r, p, q) * 0.5) + 0.5);        printf("%d\n", res);    }    return 0;}