poj1329Circle Through Three Points(三角形外接圆）

链接

套模板

不知道有没有x,y=0情况，不过这种情况都按+号输出的。

 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<vector>
 #include<cmath>
 #include<queue>
 #include<set>
 using namespace std;
 #define N 100000
 #define LL long long
 #define INF 0xfffffff
 const double eps = 1e-;
 const double pi = acos(-1.0);
 const double inf = ~0u>>;
 struct Point
 {
     double x,y;
     Point (double x=,double y =):x(x),y(y){}
 }p[];
 struct Circle
 {
     Point center;
     double r;
 };
 typedef Point pointt;
 pointt operator - (Point a,Point b)
 {
     return Point(a.x-b.x,a.y-b.y);
 }
 int dcmp(double x)
 {
     if(fabs(x)<eps) return ;
     return x<?-:;
 }
 double dis(Point a)
 {
     return a.x*a.x+a.y*a.y;
 }
 double cross(Point a,Point b)
 {
     return a.x*b.y-a.y*b.x;
 }
 double area()
 {
     return fabs(cross(p[]-p[],p[]-p[]))/;
 }
 struct Circle Circumcircle()
 {
     Circle tmp;
     double a,b,c,c1,c2;
     double xa,ya,xb,yb,xc,yc;
     a = sqrt(dis(p[]-p[]));
     b = sqrt(dis(p[]-p[]));
     c = sqrt(dis(p[]-p[]));
     //根据s = a*b*c/R/4，求半径
     tmp.r = (a*b*c)/(area()*4.0);
     xa = p[].x;
     ya = p[].y;
     xb = p[].x;
     yb = p[].y;
     xc = p[].x;
     yc = p[].y;
     c1 = (dis(p[])-dis(p[]))/;
     c2 = (dis(p[])-dis(p[]))/;
     tmp.center.x = (c1*(ya-yc)-c2*(ya-yb))/((xa-xb)*(ya-yc)-(xa-xc)*(ya-yb));
     tmp.center.y = (c1*(xa-xc)-c2*(xa-xb))/((ya-yb)*(xa-xc)-(ya-yc)*(xa-xb));
     return tmp;
 }
 int main()
 {
     while(scanf("%lf%lf%lf%lf%lf%lf",&p[].x,&p[].y,&p[].x,&p[].y,&p[].x,&p[].y)!=EOF)
     {
         Circle cc = Circumcircle();
         double r = cc.r;
         char c1,c2;
         c1 = dcmp(cc.center.x)>?'-':'+';
         c2 = dcmp(cc.center.y)>?'-':'+';
         printf("(x %c %.3f)^2 + (y %c %.3f)^2 = %.3f^2\n",c1,fabs(cc.center.x),c2,fabs(cc.center.y),r);
         double s = r*r-cc.center.x*cc.center.x-cc.center.y*cc.center.y;
         char c3 = dcmp(s)>?'-':'+';
         printf("x^2 + y^2 %c %.3fx %c %.3fy %c %.3f = 0\n",c1,fabs(cc.center.x*),c2,fabs(cc.center.y*),c3,fabs(s));
         puts("");
     }
     return ;
 }