uva 10250 - The Other Two Trees

用旋转向量

#include<iostream>#include<stdio.h>using namespace std;int main(){    double x1,y1,x2,y2,x3,y3,x4,y4,cx,cy;    while(scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2)!=EOF)    {        if(x1==x2 && y1==y2)            printf("Impossible.\n");        else        {            cx=(x1+x2)/2;            cy=(y1+y2)/2;            x1-=cx;            x2-=cx;            y1-=cy;            y2-=cy;            x3=-y1;            y3=x1;            x4=-x3;            y4=-y3;            printf("%lf %lf %lf %lf\n",x3+cx,y3+cy,x4+cx,y4+cy);        }    }    return 0;}