Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của flashmt

Code mẫu của happyboy99x

#include<bits/stdc++.h>
using namespace std;

typedef complex<double> Point;

const int N = 200, MAX = 1e5;
Point p[N];
int n;

void enter() {
    cin >> n;
    for(int i = 0; i < n; ++i)
        cin >> real(p[i]) >> imag(p[i]);
}

double minRadius(const Point &center) {
    double res = 0;
    for(int i = 0; i < n; ++i)
        res = max(res, abs(center - p[i]));
    return res;
}

double f(double x) {
    double low = -MAX, high = MAX;

    for(int t = 0; t < 75; ++t) {
        double m1 = (2 * low + high) / 3, m2 = (low + 2 * high) / 3;
        if(minRadius(Point(x, m1)) < minRadius(Point(x, m2))) high = m2;
        else low = m1;
    }

    return minRadius(Point(x, (low + high) / 2));
}

void solve() {
    double low = -MAX, high = MAX;

    for(int t = 0; t < 75; ++t) {
        double m1 = (2 * low + high) / 3, m2 = (low + 2 * high) / 3;
        if(f(m1) < f(m2)) high = m2;
        else low = m1;
    }

    cout << fixed << setprecision(6) << f((low + high) / 2) << endl;
}

int main() {
    ios::sync_with_stdio(false);
    enter();
    solve();
    return 0;
}

Code mẫu của ladpro98

#include <bits/stdc++.h>
#define X first
#define Y second
#define sqr(a) ((a) * (a))

const int N = 200;
const int INF = 1e9;
const int LIMIT = 60;

using namespace std;

typedef pair<double, double> point;

int n;
point a[N];

double dist(const point &a, const point &b) {
    return sqr(a.X - b.X) + sqr(a.Y - b.Y);
}

double evaluate(point C) {
    double ans = 0;
    for (int i = 0; i < n; ++i)
        ans = max(ans, dist(C, a[i]));
    return ans;
}

double ternarySearchY(double x) {
    double ans = INF;
    double l = -1e4, r = 1e4;
    for (int loop = 0; loop < LIMIT; ++loop) {
        double tl = l + (r - l) / 3;
        double tr = r - (r - l) / 3;
        double vl = evaluate(point(x, tl));
        double vr = evaluate(point(x, tr));
        ans = min(ans, min(vl, vr));
        if (vl < vr)
            r = tr;
        else
            l = tl;
    }
    return ans;
}

double ternarySearchX() {
    double ans = INF;
    double l = -1e4, r = 1e4;
    for (int loop = 0; loop < LIMIT; ++loop) {
        double tl = l + (r - l) / 3;
        double tr = r - (r - l) / 3;
        double vl = ternarySearchY(tl);
        double vr = ternarySearchY(tr);
        ans = min(ans, min(vl, vr));
        if (vl < vr)
            r = tr;
        else
            l = tl;
    }
    return ans;
}

int main() {
    ios::sync_with_stdio(0); cin.tie(0);
    cin >> n;
    for (int i = 0; i < n; ++i)
        cin >> a[i].X >> a[i].Y;
    double ans = ternarySearchX();
    cout << setprecision(6) << fixed << sqrt(ans) << endl;
    return 0;
}

Code mẫu của RR

//Written by RR

{$MODE OBJFPC}

uses math;
const
  FINP          =       '';
  FOUT          =       '';
  MAXN          =       100111;
  eps           =       1e-9;

type
  point         =       record x,y:double; end;
  circle        =       record x,y,r:double; end;

var
  f1,f2         :       text;
  test,n        :       longint;
  a             :       array[1..MAXN] of point;
  res           :       circle;

procedure openF;
    begin
      assign(f1,FINP); reset(f1);
      assign(f2,FOUT); rewrite(f2);
    end;

procedure closeF;
    begin
      close(f1);
      close(f2);
    end;

procedure inp;
    var
      i:longint;
    begin
      read(f1,n);
      for i:=1 to n do
        with a[i] do
          read(f1,x,y);
    end;

procedure update2(a,b:point);
    begin
      res.x:=(a.x+b.x)/2;
      res.y:=(a.y+b.y)/2;
      res.r:=sqr(a.x-res.x) + sqr(a.y-res.y);
    end;

procedure update3(a,b,c:point);
    var
      s,u,v:double;
    begin
      u:=(c.y-b.y)/2-(c.x-b.x)*(a.x-b.x)/2/(b.y-a.y);
      v:=(c.y-a.y)*(a.x-b.x)/(b.y-a.y)-(a.x-c.x);
      s:=u/v;
      res.x:=(a.x+c.x)/2+s*(c.y-a.y);
      res.y:=(a.y+c.y)/2+s*(a.x-c.x);
      res.r:=sqr(a.x-res.x)+sqr(a.y-res.y);
    end;

function isInside(a:point):boolean;
    begin
      exit( sqr(a.x-res.x) + sqr(a.y-res.y) < res.r+eps );
    end;

procedure solve;
    var
      i,j,k:longint;
    begin
      update2(a[1],a[2]);
      for i:=3 to n do
        if not isInside(a[i]) then
          begin
            update2(a[1],a[i]);
            for j:=1 to i-1 do
              if not isInside(a[j]) then
                begin
                  update2(a[i],a[j]);
                  for k:=1 to j-1 do
                    if not isInside(a[k]) then
                      update3(a[i],a[j],a[k]);
                end;
          end;
      writeln(f2,sqrt(res.r):0:6);
//      writeln(f2,res.x:0:2,' ',res.y:0:2);
    end;

begin
  openF;
  test := 1;
  for test:=1 to test do
    begin
      inp;
      if (n = 1) then writeln('0.000000')
      else solve;
    end;
  closeF;
end.

Code mẫu của hieult

#include <set>
#include <map>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <cassert>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <iomanip>
#include <iostream>
#include <algorithm>

using namespace std;

typedef long long ll;
typedef long double ld;
//typedef double ld;
typedef unsigned int ui;
typedef unsigned long long ull;

#define Rep(i,n) for(int i = 0; i < (n); ++i)
#define Repd(i,n) for(int i = (n)-1; i >= 0; --i)
#define For(i,a,b) for(int i = (a); i <= (b); ++i)
#define Ford(i,a,b) for(int i = (a); i >= (b); --i)
#define Fit(i,v) for(int i = (v).begin(); i != (v).end(); ++i)
#define Fitd(i,v) for(int i = (v).rbegin(); i != (v).rend(); ++i)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define sz(a) ((int)(a).size())
#define all(a) (a).begin(), (a).end()
#define ms(a,x) memset(a, x, sizeof(a))
#define nl puts("")
#define sp printf(" ")
#define ok puts("ok")
//#include <conio.h>

template<class F, class T> T convert(F a, int p = -1) { stringstream ss; if (p >= 0) ss << fixed << setprecision(p); ss << a; T r; ss >> r; return r; }
template<class T> void db(T a, int p = -1) { if (p >= 0) cout << fixed << setprecision(p); cout << a << " "; }
template<class T> T gcd(T a, T b) { T r; while (b != 0) { r = a % b; a = b; b = r; } return a; }
template<class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
template<class T> T sqr(T x) { return x * x; }
template<class T> T cube(T x) { return x * x * x; }
template<class T> struct Triple { T x, y, z; Triple() {} Triple(T _x, T _y, T _z) : x(_x), y(_y), z(_z) {} };
template<class T> Triple<T> euclid(T a, T b) { if (b == 0) return Triple<T>(1, 0, a); Triple<T> r = euclid(b, a % b); return Triple<T>(r.y, r.x - a / b * r.y, r.z); }
template<class T> int getbit(T s, int i) { return (s >> i) & 1; }
template<class T> T onbit(T s, int i) { return s | (T(1) << i); }
template<class T> T offbit(T s, int i) { return s & (~(T(1) << i)); }
template<class T> int cntbit(T s) { return s == 0 ? 0 : cntbit(s >> 1) + (s & 1); }
const int bfsz = 1 << 16; char bf[bfsz + 5]; int rsz = 0;int ptr = 0;
char gc() { if (rsz <= 0) { ptr = 0; rsz = fread(bf, 1, bfsz, stdin); if (rsz <= 0) return EOF; } --rsz; return bf[ptr++]; }
void ga(char &c) { c = EOF; while (!isalpha(c)) c = gc(); }
int gs(char s[]) { int l = 0; char c = gc(); while (isspace(c)) c = gc(); while (c != EOF && !isspace(c)) { s[l++] = c; c = gc(); } s[l] = '\0'; return l; }
template<class T> bool gi(T &v) {
    v = 0; char c = gc(); while (c != EOF && c != '-' && !isdigit(c)) c = gc(); if (c == EOF) return false; bool neg = c == '-'; if (neg) c = gc();
    while (isdigit(c)) { v = v * 10 + c - '0'; c = gc(); } if (neg) v = -v; return true;
}

const double PI = 2 * acos(0.0);
const string months[] = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
const int days[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const int dr[] = {0, 0, -1, +1};
const int dc[] = {-1, +1, 0, 0};
const int inf = (int)1e9 + 5;
const ll linf = (ll)1e16 + 5;
const ld eps = ld(1e-13);
const ll mod = 1000000007;
typedef pair<int, int> II;

#define maxn 1005

struct Point{
    ld x, y;
    Point(){};
    Point(ld _x, ld _y){
        x = _x; y = _y;
    }
}A[maxn];

int n;

ld cal(ld x, ld y){
    ld res = 0;
    Rep(i, n){
        res = max(res, sqrt(sqr(A[i].x - x) + sqr(A[i].y - y)));
    }
    return res;
}

ld f(ld x){
    ld u = -10000, v = 10000, r1, r2;
    Rep(run, 100){
        r1 = (u + u + v) / 3;
        r2 = (u + v + v) / 3;
        if(cal(x, r1) < cal(x, r2)) v = r2;
        else u = r1;
    }

    return cal(x, u);
}

int main(){
//    freopen("in.txt", "r", stdin);
//    freopen("out.txt", "w", stdout);
//    cout << "x" << endl;

    cin >> n;
    Rep(i, n){
        cin >> A[i].x >> A[i].y;
    }

    ld u = -10000, v = 10000, r1, r2;
    Rep(run, 100){
        r1 = (u + u + v) / 3;
        r2 = (u + v + v) / 3;
        if(f(r1) < f(r2)){
            v = r2;
        }
        else u = r1;
    }

    cout << fixed << setprecision(6);
    cout << f(u) << endl;


    return 0;
}