Language: C++

// need
#include <iostream>
#include <algorithm>
// data structure
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <complex>
//#include <deque>
#include <valarray>
#include <unordered_map>
#include <unordered_set>
#include <array>
// etc
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>
#include <fstream>

// input
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;MACRO_VAR_Scan(__VA_ARGS__);
template<typename T> void MACRO_VAR_Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void MACRO_VAR_Scan(First& first, Rest& ...rest) { std::cin >> first; MACRO_VAR_Scan(rest...); }
#define VEC_ROW(type, n, ...)std::vector<type> __VA_ARGS__;MACRO_VEC_ROW_Init(n, __VA_ARGS__); for(int w_=0; w_<n; ++w_){MACRO_VEC_ROW_Scan(w_, __VA_ARGS__);}
template<typename T> void MACRO_VEC_ROW_Init(int n, T& t) { t.resize(n); }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Init(int n, First& first, Rest& ...rest) { first.resize(n); MACRO_VEC_ROW_Init(n, rest...); }
template<typename T> void MACRO_VEC_ROW_Scan(int p, T& t) { std::cin >> t[p]; }
template<typename First, typename...Rest>void MACRO_VEC_ROW_Scan(int p, First& first, Rest& ...rest) { std::cin >> first[p]; MACRO_VEC_ROW_Scan(p, rest...); }
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& R:c)for(auto& w:R)std::cin>>w;
// output
template<typename T>void MACRO_OUT(const T t) { std::cout << t; }
template<typename First, typename...Rest>void MACRO_OUT(const First first, const Rest...rest) { std::cout << first << " "; MACRO_OUT(rest...); }
#define OUT(...) MACRO_OUT(__VA_ARGS__);
#define FOUT(n, dist) std::cout<<std::fixed<<std::setprecision(n)<<(dist);
#define SOUT(n, c, dist) std::cout<<std::setw(n)<<std::setfill(c)<<(dist);
#define EOUT(...) { OUT(__VA_ARGS__)BR; exit(0); }
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define SPBR(w, n) std::cout<<(w + 1 == n ? '\n' : ' ');
#define ENDL std::cout<<std::endl;
#define FLUSH std::cout<<std::flush;
#define SHOW(dist) {std::cerr << #dist << "\t: " << (dist) << "\n";}
#define SHOWVECTOR(v) {std::cerr << #v << "\t: ";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOWVECTOR2(v) {std::cerr << #v << "\t:\n";for(const auto& xxx : v){for(const auto& yyy : xxx){std::cerr << yyy << " ";}std::cerr << "\n";}}
#define SHOWQUEUE(a) {auto tmp(a);std::cerr << #a << "\t: ";while(!tmp.empty()){std::cerr << tmp.front() << " ";tmp.pop();}std::cerr << "\n";}
#define SHOWSTACK(a) {auto tmp(a);std::cerr << #a << "\t: ";while(!tmp.empty()){std::cerr << tmp.top() << " ";tmp.pop();}std::cerr << "\n";}
// utility
#define ALL(a) (a).begin(),(a).end()
#define FOR(w, a, n) for(int w=(a);w<(n);++w)
#define RFOR(w, a, n) for(int w=(n)-1;w>=(a);--w)
#define REP(w, n) for(int w=0;w<int(n);++w)
#define RREP(w, n) for(int w=int(n)-1;w>=0;--w)
#define IN(a, x, b) (a<=x && x<b)
template<class T> inline T CHMAX(T & a, const T b) { return a = (a < b) ? b : a; }
template<class T> inline T CHMIN(T& a, const T b) { return a = (a > b) ? b : a; }
// test
template<class T> using V = std::vector<T>;
template<class T> using VV = V<V<T>>;

template<typename S, typename T>
std::ostream& operator<<(std::ostream& os, std::pair<S, T> p) {
	os << "(" << p.first << ", " << p.second << ")"; return os;
}

// type/const
#define int ll
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using PAIR = std::pair<int, int>;
using PAIRLL = std::pair<ll, ll>;
constexpr int INFINT = (1 << 30) - 1;                    // 1.07x10^ 9
constexpr int INFINT_LIM = (1LL << 31) - 1;              // 2.15x10^ 9
constexpr ll INFLL = 1LL << 60;                          // 1.15x10^18
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);  // 9.22x10^18
constexpr double eps = 1e-7;
constexpr int MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;
template<class T, size_t N> void FILL(T(&a)[N], const T & val) { for (auto& x : a) x = val; }
template<class ARY, size_t N, size_t M, class T> void FILL(ARY(&a)[N][M], const T & val) { for (auto& b : a) FILL(b, val); }
template<class T> void FILL(std::vector<T> & a, const T & val) { for (auto& x : a) x = val; }
template<class ARY, class T> void FILL(std::vector<std::vector<ARY>> & a, const T & val) { for (auto& b : a) FILL(b, val); }
// ------------>8------------------------------------->8------------

using P = std::complex<ld>;
ld cross(const P& a, const P& b) { return a.real()* b.imag() - a.imag() * b.real(); }
ld dot(const P& a, const P& b) { return a.real()* b.real() + a.imag() * b.imag(); }
template <class iter>
std::pair<P, ld> min_ball(iter left, iter right, int seed = 1333) {
	const int n = right - left;

	assert(n >= 1);
	if (n == 1) {
		return { *left, ld(0) };
	}

	std::mt19937 mt(seed);
	std::shuffle(left, right, mt);
	// std::random_shuffle(left, right); // simple but deprecated

	iter ps = left;
	using circle = std::pair<P, ld>;

	auto make_circle_3 = [](const P & a, const P & b, const P & c) -> circle {
		ld A = std::norm(b - c), B = std::norm(c - a), C = std::norm(a - b),
			S = cross(b - a, c - a);
		P p = (A * (B + C - A) * a + B * (C + A - B) * b + C * (A + B - C) * c) / (4 * S * S);
		P p = (a + b + c)/ (ld)3;
        ld r2 = std::norm(p - a);
		return { p, r2 };
	};

	auto make_circle_2 = [](const P & a, const P & b) -> circle {
		P c = (a + b) / (ld)2;
		ld r2 = std::norm(a - c);
		return { c, r2 };
	};

	auto in_circle = [](const P & a, const circle & c) -> bool {
		return std::norm(a - c.first) <= c.second + eps;
	};

	circle c = make_circle_2(ps[0], ps[1]);

	// MiniDisc
	for (int i = 2; i < n; ++i) {
		if (!in_circle(ps[i], c)) {
			// MiniDiscWithPoint
			c = make_circle_2(ps[0], ps[i]);
			for (int j = 1; j < i; ++j) {
				if (!in_circle(ps[j], c)) {
					// MiniDiscWith2Points
					c = make_circle_2(ps[i], ps[j]);
					for (int k = 0; k < j; ++k) {
						if (!in_circle(ps[k], c)) {
							c = make_circle_3(ps[i], ps[j], ps[k]);
						}
					}
				}
			}
		}
	}
	return c;
}

signed main() {
	INIT;

	VAR(int, n);
	VEC_ROW(int, n, x, y);
	V<P> ps(n);
	REP(i, n) ps[i] = P(x[i], y[i]);
	auto p = min_ball(ALL(ps));
	FOUT(12, std::sqrt(p.second))BR;

	return 0;
}


Compiler output:
a.cc: In lambda function:
a.cc:120:19: error: redeclaration of 'P p'
  120 |                 P p = (a + b + c)/ (ld)3;
      |                   ^
a.cc:119:19: note: 'P p' previously declared here
  119 |                 P p = (A * (B + C - A) * a + B * (C + A - B) * b + C * (A + B - C) * c) / (4 * S * S);
      |                   ^