1659. Regular Triangles（计算几何）

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题意：给定一个等边三角形，求三角形里面三个点和三角形外的三个点，使其中的点组成的等边三角形不少于9个。

思路：让里面的三角形中的一个点在中心，然后使外面的点与给定的点和中心点构成等边三角形，，三角形个数正好是9个。

#include <cstdio>#include <cstring>#include <cmath>#include <iostream>#include <algorithm>#include <stack>#include <queue>#include <vector>#include <map>#include <string>#define LL long long#define DB doubleusing namespace std;struct cpoint{    DB x,y;    cpoint(){}    cpoint(DB a,DB b){x=a,y=b;}    void get(){scanf("%lf%lf",&x,&y);}    void out(){printf("%.10lf %.10lf\n",x,y);}};struct cvector{    DB x,y;    cvector(){}    cvector(DB a,DB b){x=a,y=b;}};cvector operator-(cpoint a,cpoint b){    return  cvector(a.x-b.x,a.y-b.y);}cpoint operator+(cpoint a,cvector b){    return cpoint(a.x+b.x,a.y+b.y);}cvector operator*(DB t,cvector a){    return cvector(t*a.x,t*a.y);}cpoint a,b,c,o;int main(){    #ifndef ONLINE_JUDGE    freopen("in.txt","r",stdin);    #endif    a.get();b.get();c.get();    o.x = (a.x+b.x+c.x)/3;    o.y = (a.y+b.y+c.y)/3;    cvector v1,v2,v3;    v1 = a-o;v2 = b-o;v3=c-o;    cpoint tmp;    o.out();    tmp = o+(-0.25)*(a-b);tmp.out();    tmp = o+(-0.25)*(c-b);tmp.out();    tmp = o+(-1.0)*v1;tmp.out();    tmp = o+(-1.0)*v2;tmp.out();    tmp = o+(-1.0)*v3;tmp.out();    return 0;}