三分 POJ 2420 A Star not a Tree?

题目传送门

 /*
     题意：求费马点
     三分：对x轴和y轴求极值，使到每个点的距离和最小
 */
 #include <cstdio>
 #include <algorithm>
 #include <cstring>
 #include <cmath>

 const int MAXN = 1e2 + ;
 const int INF = 0x3f3f3f3f;
 double x[MAXN], y[MAXN];
 int n;

 double sum(double x1, double y1)    {
     double res = ;
     for (int i=; i<=n; ++i)    {
         res += sqrt ((x1 - x[i]) * (x1 - x[i]) + (y1 - y[i]) * (y1 - y[i]));
     }
     return res;
 }

 double cal(double x1)   {
     int l = 0.0, r = 10000.0;
     for (int i=; i<=; ++i)  {
         double lmid = (l + r) / ;
         double rmid = (lmid + r) / ;
         if (sum (x1, lmid) < sum (x1, rmid))    r = rmid;
         else    l = lmid;
     }
     return sum (x1, l);
 }

 int main(void)  {       //POJ 2420 A Star not a Tree?
     //freopen ("POJ_2420.in", "r", stdin);

     while (scanf ("%d", &n) == )   {
         for (int i=; i<=n; ++i)    {
             scanf ("%lf%lf", &x[i], &y[i]);
         }

         double l = 0.0, r = 10000.0;
         for (int i=; i<=; ++i)  {
             double lmid = (l + r) / ;
             double rmid = (lmid + r) / ;
             if (cal (lmid) < cal (rmid))    r = rmid;
             else    l = lmid;
         }
         printf ("%.0f\n", cal (l));
     }

     return ;
 }