Language: C++

push_back
#define fi first
#define se second

typedef pair<ll,ll> P;
using VP = vector<P>; using VVP = vector<VP>;
using VI = vector<int>; using VVI = vector<VI>; using VVVI = vector<VVI>;
const long double inf=1e9+7;
const ll INF=1LL<<61;
const ll mod=1e9+7;

long double x[55],y[55];
long double dif(int i,int j){
  return sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
}

long double px,py;

void Circumcenter(int a,int b,int c) {

	//辺
	long double eAB = dif(a,b);
	long double eBC = dif(b,c);
	long double eCA = dif(c,a);

	//角度(余弦定理)
	long double aCAB = acos((eCA*eCA + eAB*eAB - eBC*eBC) / (2 * eCA*eAB));
	long double aABC = acos((eAB*eAB + eBC*eBC - eCA*eCA) / (2 * eAB*eBC));
	long double aBCA = acos((eBC*eBC + eCA*eCA - eAB*eAB) / (2 * eBC*eCA));

	long double A = sin(2 * aCAB);
	long double B = sin(2 * aABC);
	long double C = sin(2 * aBCA);

	//外心の位置ベクトル(ベクトルの面積比の公式)
	
	px=(A*x[a] + B*x[b] + C*x[c]) / (A + B + C);
  py=(A*y[a] + B*y[b] + C*y[c]) / (A + B + C);

} 


int main(){
  int i,j,k;
  int n;
  cin>>n;
  long double ans=inf;
  for(i=0;i<n;i++){
    cin>>x[i]>>y[i];
  }
  if(n==2){
    cout<<fixed<<setprecision(15)<<dif(0,1)/2.00<<endl;
  }
  else{
    for(i=0;i<n;i++){
      for(j=i+1;j<n;j++){
        for(k=j+1;k<n;k++){
          long double R=0;
          Circumcenter(i,j,k);
          //cout<<px<<" "<<py<<endl;
          for(int l=0;l<n;l++) R=max(R,sqrt((x[l]-px)*(x[l]-px)+(y[l]-py)*(y[l]-py)));
          ans=min(ans,R);
        }
      }
    }
    cout<<fixed<<setprecision(15)<<ans<<endl;
  }
  
  return 0;
}


Compiler output:
a.cc:1:1: error: 'push_back' does not name a type
    1 | push_back
      | ^~~~~~~~~
a.cc:6:12: error: 'vector' does not name a type
    6 | using VP = vector<P>; using VVP = vector<VP>;
      |            ^~~~~~
a.cc:6:35: error: 'vector' does not name a type
    6 | using VP = vector<P>; using VVP = vector<VP>;
      |                                   ^~~~~~
a.cc:7:12: error: 'vector' does not name a type
    7 | using VI = vector<int>; using VVI = vector<VI>; using VVVI = vector<VVI>;
      |            ^~~~~~
a.cc:7:37: error: 'vector' does not name a type
    7 | using VI = vector<int>; using VVI = vector<VI>; using VVVI = vector<VVI>;
      |                                     ^~~~~~
a.cc:7:62: error: 'vector' does not name a type
    7 | using VI = vector<int>; using VVI = vector<VI>; using VVVI = vector<VVI>;
      |                                                              ^~~~~~
a.cc:9:7: error: 'll' does not name a type
    9 | const ll INF=1LL<<61;
      |       ^~
a.cc:10:7: error: 'll' does not name a type
   10 | const ll mod=1e9+7;
      |       ^~
a.cc: In function 'long double dif(int, int)':
a.cc:14:10: error: 'sqrt' was not declared in this scope
   14 |   return sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
      |          ^~~~
a.cc: In function 'void Circumcenter(int, int, int)':
a.cc:27:28: error: 'acos' was not declared in this scope
   27 |         long double aCAB = acos((eCA*eCA + eAB*eAB - eBC*eBC) / (2 * eCA*eAB));
      |                            ^~~~
a.cc:31:25: error: 'sin' was not declared in this scope
   31 |         long double A = sin(2 * aCAB);
      |                         ^~~
a.cc: In function 'int main()':
a.cc:46:3: error: 'cin' was not declared in this scope
   46 |   cin>>n;
      |   ^~~
a.cc:52:5: error: 'cout' was not declared in this scope
   52 |     cout<<fixed<<setprecision(15)<<dif(0,1)/2.00<<endl;
      |     ^~~~
a.cc:52:11: error: 'fixed' was not declared in this scope
   52 |     cout<<fixed<<setprecision(15)<<dif(0,1)/2.00<<endl;
      |           ^~~~~
a.cc:52:18: error: 'setprecision' was not declared in this scope
   52 |     cout<<fixed<<setprecision(15)<<dif(0,1)/2.00<<endl;
      |                  ^~~~~~~~~~~~
a.cc:52:51: error: 'endl' was not declared in this scope
   52 |     cout<<fixed<<setprecision(15)<<dif(0,1)/2.00<<endl;
      |                                                   ^~~~
a.cc:61:40: error: 'sqrt' was not declared in this scope
   61 |           for(int l=0;l<n;l++) R=max(R,sqrt((x[l]-px)*(x[l]-px)+(y[l]-py)*(y[l]-py)));
      |                                        ^~~~
a.cc:61:34: error: 'max' was not declared in this scope
   61 |           for(int l=0;l<n;l++) R=max(R,sqrt((x[l]-px)*(x[l]-px)+(y[l]-py)*(y[l]-py)));
      |                                  ^~~
a.cc:62:15: error: 'min' was not declared in this scope; did you mean 'main'?
   62 |           ans=min(ans,R);
      |               ^~~
      |               main
a.cc:66:5: error: 'cout' was not declared in this scope
   66 |     cout<<fixed<<setprecision(15)<<ans<<endl;
      |     ^~~~
a.cc:66:11: error: 'fixed' was not declared in this scope
   66 |     cout<<fixed<<setprecision(15)<<ans<<endl;
      |           ^~~~~
a.cc:66:18: error: 'setprecision' was not declared in this scope
   66 |     cout<<fixed<<setprecision(15)<<ans<<endl;
      |                  ^~~~~~~~~~~~
a.cc:66:41: error: 'endl' was not declared in this scope
   66 |     cout<<fixed<<setprecision(15)<<ans<<endl;
      |                                         ^~~~