Language: C++

 **********************************/
#include <stdio.h>
#include <cstdio>
#include <iostream>
#include <iomanip>
#include <queue>
#include <set>
#include <vector>
#include <string>
#include <cstring>
#include <algorithm>
#include <cmath>

double delta = 1e-7;

int main(){
  long long int N;
  double tmp1, tmp2;
  scanf("%lld", &N);

  std::vector<double> x, y;
  for(long long int i = 0; i < N; i++){
    scanf("%lf%lf", &tmp1, &tmp2);
    x.push_back(tmp1);
    y.push_back(tmp2);
  }


  if(N==2){
    std::cerr << "Answer: " << std::endl;
    std::cout << std::sqrt((x[0]-x[1])*(x[0]-x[1]) + (y[0]-x[1])*(y[0]-y[1]))*0.5 << std::endl;
    return 0;
  }

  double lij, ljk, lki;
  double a, b, c, d, e, f;
  double aa, bb, cc, dd, ee, ff;
  double r, px, py;
  long long int flg = 0;
  double ans = 1.0e9;
  for(long long int i = 0; i < N; i++){
    for(long long int j = i+1; j < N; j++){
      for(long long int k = j+1; k < N; k++){
        lij = ((x[i]-x[j])*(x[i]-x[j]) + (y[i]-y[j])*(y[i]-y[j]));
        ljk = ((x[j]-x[k])*(x[j]-x[k]) + (y[j]-y[k])*(y[j]-y[k]));
        lki = ((x[k]-x[i])*(x[k]-x[i]) + (y[k]-y[i])*(y[k]-y[i]));

        /*if(lij > ljk+lki){
          px = 0.5 * (x[i]+x[j]);
          py = 0.5 * (y[i]+y[j]);
          r = std::sqrt(lij)*0.5;
        }
        else if(ljk > lij+lki){
          px = 0.5 * (x[k]+x[j]);
          py = 0.5 * (y[k]+y[j]);
          r = std::sqrt(ljk)*0.5;
        }
        else if(lki > lij + ljk){
          px = 0.5 * (x[k]+x[i]);
          py = 0.5 * (y[k]+y[i]);
          r = std::sqrt(lki)*0.5;
        }
        else*/{
        
        a = x[i];
        b = y[i];
        c = x[j];
        d = y[j];
        e = x[k];
        f = y[k];
        aa = a * a;
        bb = b * b;
        cc = c * c;
        dd = d * d;
        ee = e * e;
        ff = f * f;

        py = ((e - a) * (aa + bb - cc - dd) - (c - a) * (aa + bb - ee- ff)) / (2 * (e - a)*(b - d) - 2 * (c - a) * (b - f));

        if(std::abs(c-a) < 0.5){
          px = (2 * (b - f) * py - aa - bb + ee + ff) / (2 * (e - a));
        }
        else
          px = (2 * (b - d) * py - aa - bb + cc + dd) / (2 * (c - a));

        r = std::sqrt((px - a)*(px - a) + (py - b)*(py - b));
        }

        flg = 1;
        for(long long int l = 0; l < N; l++){
          
          if(l == i || l ==j || l == k){
            continue;
          }
          if((x[l]-px)*(x[l]-px) + (y[l]-py)*(y[l]-py) > r*r+delta){
            flg = 0;
            break;
          }
        }
        if(flg == 1){
          ans = std::min(ans, r);
        }
      }
    }
  }

  for(long long int i = 0; i < N; i++){
    for(long long int j = i+1; j < N; j++){
      for(long long int k = j+1; k < N; k++){
        lij = ((x[i]-x[j])*(x[i]-x[j]) + (y[i]-y[j])*(y[i]-y[j]));
        ljk = ((x[j]-x[k])*(x[j]-x[k]) + (y[j]-y[k])*(y[j]-y[k]));
        lki = ((x[k]-x[i])*(x[k]-x[i]) + (y[k]-y[i])*(y[k]-y[i]));

        flg = 0;
        if(lij > ljk+lki){
          px = 0.5 * (x[i]+x[j]);
          py = 0.5 * (y[i]+y[j]);
          r = std::sqrt(lij)*0.5;
          flg = 1;
        }
        else if(ljk > lij+lki){
          px = 0.5 * (x[k]+x[j]);
          py = 0.5 * (y[k]+y[j]);
          r = std::sqrt(ljk)*0.5;
          flg = 1;
        }
        else if(lki > lij + ljk){
          px = 0.5 * (x[k]+x[i]);
          py = 0.5 * (y[k]+y[i]);
          r = std::sqrt(lki)*0.5;
          flg = 1;
        }

        if(flg == 0)continue;

        flg = 1;
        for(long long int l = 0; l < N; l++){
          
          if(l == i || l ==j || l == k){
            continue;
          }
          if((x[l]-px)*(x[l]-px) + (y[l]-py)*(y[l]-py) > r*r+delta){
            flg = 0;
            break;
          }
        }
        if(flg == 1){
          ans = std::min(ans, r);
        }
      }
    }
  }
  

  std::cerr << "Answer: " << std::endl;
  std::cout << std::setprecision(10) << ans << std::endl;

  return 0;
}

Compiler output:
a.cc:1:36: error: expected unqualified-id before '/' token
    1 |  **********************************/
      |                                    ^
In file included from a.cc:3:
/usr/include/c++/14/cstdio:98:11: error: 'FILE' has not been declared in '::'
   98 |   using ::FILE;
      |           ^~~~
/usr/include/c++/14/cstdio:99:11: error: 'fpos_t' has not been declared in '::'
   99 |   using ::fpos_t;
      |           ^~~~~~
/usr/include/c++/14/cstdio:101:11: error: 'clearerr' has not been declared in '::'
  101 |   using ::clearerr;
      |           ^~~~~~~~
/usr/include/c++/14/cstdio:102:11: error: 'fclose' has not been declared in '::'
  102 |   using ::fclose;
      |           ^~~~~~
/usr/include/c++/14/cstdio:103:11: error: 'feof' has not been declared in '::'
  103 |   using ::feof;
      |           ^~~~
/usr/include/c++/14/cstdio:104:11: error: 'ferror' has not been declared in '::'
  104 |   using ::ferror;
      |           ^~~~~~
/usr/include/c++/14/cstdio:105:11: error: 'fflush' has not been declared in '::'
  105 |   using ::fflush;
      |           ^~~~~~
/usr/include/c++/14/cstdio:106:11: error: 'fgetc' has not been declared in '::'
  106 |   using ::fgetc;
      |           ^~~~~
/usr/include/c++/14/cstdio:107:11: error: 'fgetpos' has not been declared in '::'
  107 |   using ::fgetpos;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:108:11: error: 'fgets' has not been declared in '::'
  108 |   using ::fgets;
      |           ^~~~~
/usr/include/c++/14/cstdio:109:11: error: 'fopen' has not been declared in '::'
  109 |   using ::fopen;
      |           ^~~~~
/usr/include/c++/14/cstdio:110:11: error: 'fprintf' has not been declared in '::'
  110 |   using ::fprintf;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:111:11: error: 'fputc' has not been declared in '::'
  111 |   using ::fputc;
      |           ^~~~~
/usr/include/c++/14/cstdio:112:11: error: 'fputs' has not been declared in '::'
  112 |   using ::fputs;
      |           ^~~~~
/usr/include/c++/14/cstdio:113:11: error: 'fread' has not been declared in '::'
  113 |   using ::fread;
      |           ^~~~~
/usr/include/c++/14/cstdio:114:11: error: 'freopen' has not been declared in '::'
  114 |   using ::freopen;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:115:11: error: 'fscanf' has not been declared in '::'
  115 |   using ::fscanf;
      |           ^~~~~~
/usr/include/c++/14/cstdio:116:11: error: 'fseek' has not been declared in '::'
  116 |   using ::fseek;
      |           ^~~~~
/usr/include/c++/14/cstdio:117:11: error: 'fsetpos' has not been declared in '::'
  117 |   using ::fsetpos;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:118:11: error: 'ftell' has not been declared in '::'
  118 |   using ::ftell;
      |           ^~~~~
/usr/include/c++/14/cstdio:119:11: error: 'fwrite' has not been declared in '::'
  119 |   using ::fwrite;
      |           ^~~~~~
/usr/include/c++/14/cstdio:120:11: error: 'getc' has not been declared in '::'
  120 |   using ::getc;
      |           ^~~~
/usr/include/c++/14/cstdio:121:11: error: 'getchar' has not been declared in '::'
  121 |   using ::getchar;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:126:11: error: 'perror' has not been declared in '::'
  126 |   using ::perror;
      |           ^~~~~~
/usr/include/c++/14/cstdio:127:11: error: 'printf' has not been declared in '::'
  127 |   using ::printf;
      |           ^~~~~~
/usr/include/c++/14/cstdio:128:11: error: 'putc' has not been declared in '::'
  128 |   using ::putc;
      |           ^~~~
/usr/include/c++/14/cstdio:129:11: error: 'putchar' has not been declared in '::'
  129 |   using ::putchar;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:130:11: error: 'puts' has not been declared in '::'
  130 |   using ::puts;
      |           ^~~~
/usr/include/c++/14/cstdio:131:11: error: 'remove' has not been declared in '::'
  131 |   using ::remove;
      |           ^~~~~~
/usr/include/c++/14/cstdio:132:11: error: 'rename' has not been declared in '::'
  132 |   using ::rename;
      |           ^~~~~~
/usr/include/c++/14/cstdio:133:11: error: 'rewind' has not been declared in '::'
  133 |   using ::rewind;
      |           ^~~~~~
/usr/include/c++/14/cstdio:134:11: error: 'scanf' has not been declared in '::'
  134 |   using ::scanf;
      |           ^~~~~
/usr/include/c++/14/cstdio:135:11: error: 'setbuf' has not been declared in '::'
  135 |   using ::setbuf;
      |           ^~~~~~
/usr/include/c++/14/cstdio:136:11: error: 'setvbuf' has not been declared in '::'
  136 |   using ::setvbuf;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:137:11: error: 'sprintf' has not been declared in '::'
  137 |   using ::sprintf;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:138:11: error: 'sscanf' has not been declared in '::'
  138 |   using ::sscanf;
      |           ^~~~~~
/usr/include/c++/14/cstdio:139:11: error: 'tmpfile' has not been declared in '::'
  139 |   using ::tmpfile;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:141:11: error: 'tmpnam' has not been declared in '::'
  141 |   using ::tmpnam;
      |           ^~~~~~
/usr/include/c++/14/cstdio:143:11: error: 'ungetc' has not been declared in '::'
  143 |   using ::ungetc;
      |           ^~~~~~
/usr/include/c++/14/cstdio:144:11: error: 'vfprintf' has not been declared in '::'
  144 |   using ::vfprintf;
      |           ^~~~~~~~
/usr/include/c++/14/cstdio:145:11: error: 'vprintf' has not been declared in '::'
  145 |   using ::vprintf;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:146:11: error: 'vsprintf' has not been declared in '::'
  146 |   using ::vsprintf;
      |           ^~~~~~~~
/usr/include/c++/14/cstdio:175:11: error: 'snprintf' has not been declared in '::'
  175 |   using ::snprintf;
      |           ^~~~~~~~
/usr/include/c++/14/cstdio:176:11: error: 'vfscanf' has not been declared in '::'
  176 |   using ::vfscanf;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:177:11: error: 'vscanf' has not been declared in '::'
  177 |   using ::vscanf;
      |           ^~~~~~
/usr/include/c++/14/cstdio:178:11: error: 'vsnprintf' has not been declared in '::'
  178 |   using ::vsnprintf;
      |           ^~~~~~~~~
/usr/include/c++/14/cstdio:179:11: error: 'vsscanf' has not been declared in '::'
  179 |   using ::vsscanf;
      |           ^~~~~~~
/usr/include/c++/14/cstdio:185:22: error: 'snprintf' has not been declared in '__gnu_cxx'
  185 |   using ::__gnu_cxx::snprintf;
      |                      ^~~~~~~~
/usr/include/c++/14/cstdio:186:22: error: 'vfscanf' has not been declared in '__gnu_cxx'
  186 |   using ::__gnu_cxx::vfscanf;
      |                      ^~~~~~~
/usr/include/c++/14/cstdio:187:22: error: 'vscanf' has not been declared in '__gnu_cxx'
  187 |   using ::__gnu_cxx::vscanf;
      |                      ^~~~~~
/usr/include/c++/14/cstdio:188:22: error: 'vsnprintf' has not been declared in '__gnu_cxx'
  188 |   using ::__gnu_cxx::vsnprintf;
      |                      ^~~~~~~~~
/usr/include/c++/14/cstdio:189:22: error: 'vsscanf' has not been declared in '__gnu_cxx'
  189 |   using ::__gnu_cxx::vsscanf;
      |                      ^~~~~~~
In file included from /usr/include/wchar.h:53,
                 from /usr/include/c++/14/cwchar:44,
                 from /usr/include/c++/14/bits/postypes.h:40,
                 from /usr/include/c++/14/iosfwd:42,
                 from /usr/include/c++/14/ios:40,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:4:
/usr/include/x86_64-linux-gnu/bits/types/mbstate_t.h:6:9: error: '__mbstate_t' does not name a type
    6 | typedef __mbstate_t mbstate_t;
      |         ^~~~~~~~~~~
/usr/include/wchar.h:104:59: error: 'size_t' has not been declared
  104 |                          const wchar_t *__restrict __src, size_t __n)
      |                                                           ^~~~~~
/usr/include/wchar.h:109:8: error: 'size_t' does not name a type
  109 | extern size_t wcslcpy (wchar_t *__restrict __dest,
      |        ^~~~~~
/usr/include/wchar.h:61:1: note: 'size_t' is defined in header '<cstddef>'; this is probably fixable by adding '#include <cstddef>'
   60 | # include <bits/types/locale_t.h>
  +++ |+#include <cstddef>
   61 | #endif
/usr/include/wchar.h:115:8: error: 'size_t' does not name a type
  115 | extern size_t wcslcat (wchar_t *__restrict __dest,
      |        ^~~~~~
/usr/include/wchar.h:115:8: note: 'size_t' is defined in header '<cstddef>'; this is probably fixable by adding '#include <cstddef>'
/usr/include/wchar.h:126:59: error: 'size_t' has not been declared
  126 |                          const wchar_t *__restrict __src, size_t __n)
      |                                                           ^~~~~~
/usr/include/wchar.h:133:63: error: 'size_t' has not been declared
  133 | extern int wcsncmp (const wchar_t *__s1, const wchar_t *__s2, size_t __n)
      |                                                               ^~~~~~
/usr/include/wchar.h:142:25: error: 'size_t' has not been declared
  142 |                         size_t __n) __THROW;
      |                         ^~~~~~
/usr/include/wchar.h:150:27: error: 'size_t' has not been declared
  150 |                           size_t __n, locale_t __loc) __THROW;
      |                           ^~~~~~
/usr/include/wchar.h:159:8: error: 'size_t' does not name a type
  159 | extern size_t wcsxfrm (wchar_t *__restrict __s1,
      |        ^~~~~~
/usr/include/wchar.h:159:8: note: 'size_t' is defined in header '<cstddef>'; this is probably fixable by adding '#include <cstddef>'
/usr/include/wchar.h:174:8: error: 'size_t' does not name a type
  174 | extern size_t wcsxfrm_l (wchar_t *__s1, const wchar_t *__s2,
      |        ^~~~~~
/usr/include/wchar.h:174:8: note: 'size_t' is defined in header '<cstddef>'; this is probably fixable by adding '#include <cstddef>'
/usr/include/wchar.h:212:8: error: 'size_t' does not name a type
  212 | extern size_t wcscspn (const wchar_t *__wcs, const wchar_t *__reject)
      |        ^~~~~~
/usr/include/wchar.h:212:8: note: 'size_t' is defined in header '<cstddef>'; th