计算几何 HDOJ 4720 Naive and Silly Muggles

题目传送门

/*
    题意：给三个点求它们的外接圆，判断一个点是否在园内
    计算几何：我用重心当圆心竟然AC了，数据真水:)
    正解以后补充，http://www.cnblogs.com/kuangbin/archive/2013/09/11/3315055.html
*/
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <string>
#include <cmath>
using namespace std;

int main(void)        //HDOJ 4720 Naive and Silly Muggles
{
    //freopen ("E.in", "r", stdin);

    double x1, y1, x2, y2, x3, y3, xq, yq;
    double x0, y0;
    double r;
    double d;
    int t, cas = 0;

    scanf ("%d", &t);
    while (t--)
    {
        scanf ("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3);
        scanf ("%lf%lf", &xq, &yq);
        x0 = (x1 + x2 + x3) / 3.0;
        y0 = (y1 + y2 + y3) / 3.0;
        r = (x1 - x0) * (x1 - x0) + (y1 - y0) * (y1 - y0);
        d = (xq - x0) * (xq - x0) + (yq - y0) * (yq - y0);

        printf ("Case #%d: ", ++cas);
        if (d <= r)    puts ("Danger");
        else    puts ("Safe");
    }

    return 0;
}

/*
Case #1: Danger
Case #2: Safe
Case #3: Safe
*/