HDU 3007

基本小圆覆盖模板题

#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;
int X,Y; int n;
const double eps=0.00000001;
struct point{
    double x,y;
}p[550];

struct Circle{
    point cent;
    double r;
}cir;

double dist(point x, point y){
    double a=x.x-y.x;
    double b=x.y-y.y;
    return sqrt(a*a+b*b);
}

double triangleArea(point t1, point t2, point t3){
    point p1,p2;
    p1.x=t2.x-t1.x; p1.y=t2.y-t1.y;
    p2.x=t3.x-t1.x; p2.y=t3.y-t1.y;
    return fabs(p1.x*p2.y-p1.y*p2.x)/2;
}

Circle triangleCircle(point t1, point t2, point t3){
    Circle tmp;
    double a=dist(t1,t2);
    double b=dist(t2,t3);
    double c=dist(t3,t1);
    tmp.r=a*b*c/triangleArea(t1,t2,t3)/4;
    double xa,ya,xb,yb,xc,yc;
    double c1,c2;
    xa=t1.x; ya= t1.y;
    xb=t2.x; yb= t2.y;
    xc=t3.x; yc= t3.y;
    c1=(xa*xa+ya*ya-xb*xb-yb*yb)/2;
    c2=(xa*xa+ya*ya-xc*xc-yc*yc)/2;
    tmp.cent.x=(c1*(ya-yc)-c2*(ya-yb))/((xa-xb)*(ya-yc)-(xa-xc)*(ya-yb));
    tmp.cent.y=(c1*(xa-xc)-c2*(xa-xb))/((ya-yb)*(xa-xc)-(ya-yc)*(xa-xb));
    return tmp;
}

void slove(){
    random_shuffle(p,p+n);
    cir.cent=p[0];
    cir.r=0;
    for(int i=1;i<n;i++){
        if(dist(cir.cent,p[i])>cir.r){
            cir.cent=p[i]; cir.r=0;
            for(int j=0;j<i;j++){
                if(dist(cir.cent,p[j])>cir.r){
                    cir.cent.x=(p[i].x+p[j].x)/2;
                    cir.cent.y=(p[i].y+p[j].y)/2;
                    cir.r=dist(p[i],p[j])/2;
                    for(int k=0;k<j;k++){
                        if(dist(cir.cent,p[k])>cir.r){
                            cir=triangleCircle(p[i],p[j],p[k]);
                        }
                    }
                }
            }
        }
    }
}

int main (){
    while(scanf("%d",&n),n){
        for(int i=0;i<n;i++){
            scanf("%lf%lf",&p[i].x,&p[i].y);
        }
        slove();
        printf("%0.2lf %0.2lf ",cir.cent.x,cir.cent.y);
        printf("%0.2lf\n",cir.r);
    }
    return 0;
}