UVA 11178 Morley's Theorem（旋转+直线交点）

题目链接：http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=18543

【思路】

       旋转+直线交点

       第一个计算几何题，照着书上代码打的。

【代码】

#include<cstdio>
#include<cmath>
#include<cstring>
using namespace std;


struct Pt { 
    double x,y;
    Pt(double x=0,double y=0):x(x),y(y) {}
};
typedef Pt vec;

vec operator - (Pt A,Pt B) { return vec(A.x-B.x,A.y-B.y); }
vec operator + (vec A,vec B) { return vec(A.x+B.x,A.y+B.y); }
vec operator * (vec A,double p) { return vec(A.x*p , A.y*p); }

double cross(vec A,vec B) { return A.x*B.y-A.y*B.x; }
double Dot(vec A,vec B) { return A.x*B.x+A.y*B.y; }
double Len(vec A) { return sqrt(Dot(A,A)); }
double Angle(vec A,vec B) { return acos(Dot(A,B)/Len(A)/Len(B)); }

vec rotate(vec A,double rad) { 
    return vec(A.x*cos(rad)-A.y*sin(rad) , A.x*sin(rad)+A.y*cos(rad));
}
Pt LineIntersection(Pt P,vec v,Pt Q,vec w) {
    vec u=P-Q;
    double t=cross(w,u)/cross(v,w);
    return P+v*t;
}
Pt getD(Pt A,Pt B,Pt C) {
    vec v1=C-B;
    double a=Angle(A-B,v1);
    v1=rotate(v1,a/3);
    vec v2=B-C;
    a=Angle(A-C,v2);
    v2=rotate(v2,-a/3);
    return LineIntersection(B,v1,C,v2);
}
Pt read() {
    double x,y;
    scanf("%lf%lf",&x,&y);
    return Pt(x,y);
}
int main() {
    Pt A,B,C,D,E,F;
    int T;
    scanf("%d",&T);
    while(T--) {
        A=read() , B=read() , C=read();
        D=getD(A,B,C);
        E=getD(B,C,A);
        F=getD(C,A,B);
        printf("%.6lf %.6lf %.6lf %.6lf %.6lf %.6lf
",D.x,D.y,E.x,E.y,F.x,F.y);
    }
    return 0;
}