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

Code mẫu của ladpro98

#include <iostream>
#include <iomanip>
#include <cstdio>
#include <algorithm>
#define ii pair<int, int>
#define X first
#define Y second
const int N = 50005;
using namespace std;
ii a[N], H[N];
int n, k;

void operator -= (ii &A, ii B) {A.X -= B.X; A.Y -= B.Y;}
bool ccw(ii A, ii B, ii C) {C -= B; B -= A; return B.X * C.Y >= B.Y * C.X;}
int area(int i, int j, int k) 
    {return abs(H[i].X * (H[j].Y - H[k].Y) + H[j].X * (H[k].Y - H[i].Y) + H[k].X * (H[i].Y - H[j].Y));}

int Find(int l, int r) {
    int ll = l, rr = r, S = 0;
    while (ll < rr) {
        int m = ll + rr >> 1;
        int p = area(l, m, r), q = area(l, m + 1, r);
        if (p <= q) 
            ll = m + 1;
        else 
            rr = m;
        S = max(S, max(p, q));
    }
    return S;
}

int Search(int l, int r) {
    int ll = l + 1, rr = r - 1, S = 0;
    while (ll < rr) {
        int m = ll + rr >> 1;
        int p = Find(l, m), q = Find(l, m + 1);
        if (p <= q) 
            ll = m + 1;
        else
            rr = m;
        S = max(S, max(p, q));
    }
    return S;
}

int main() {
    ios :: sync_with_stdio(0); cin.tie(0);
    while (cin >> n) {
        if (n == -1) break;
        for(int i = 0; i < n; i++)
            cin >> a[i].X >> a[i].Y;
        sort(a, a + n);
        int k = 0;
        for(int i = 0; i < n; i++) {
            while (k >= 2 && ccw(H[k - 2], H[k - 1], a[i])) k--;
            H[k++] = a[i];
        }
        for(int i = n - 2, t = k + 1; i >= 0; i--) {
            while (k >= t && ccw(H[k - 2], H[k - 1], a[i])) k--;
            H[k++] = a[i];
        }
        k--;
        int res = 0;
        for(int i = 0; i < k; i++) 
            res = max(res, Search(i, k));
        cout << setprecision(2) << fixed << (double)res / 2 << '\n';
    }
    return 0;
}

Code mẫu của RR

//Written by Nguyen Thanh Trung
{$R+,Q+}
{$Mode objFPC}
uses math;
const
  FINP          =       '';
  FOUT          =       '';
  MAXN          =       50111;
  eps           =       1e-6;
type
  point         =       record x,y:longint; end;
var
  f1,f2         :       text;
  n             :       longint;
  a,ch          :       array[0..MAXN] of point;

procedure openF;
    begin
      assign(f1,FINP); reset(f1);
      assign(f2,FOUT); rewrite(f2);
    end;
procedure closeF;
    begin
      close(f1);
      close(f2);
    end;
procedure swap(var a,b:point); inline;
    var
      temp:point;
    begin
      temp:=a; a:=b; b:=temp;
    end;
function CCW(p1,p2,p3:point):longint;
    var
      a1,a2,b1,b2,c1,c2,t:double;
    begin
      a1:=p2.x-p1.x;
      b1:=p2.y-p1.y;
      a2:=p3.x-p2.x;
      b2:=p3.y-p2.y;
      t:=a1*b2-a2*b1;
      if abs(t)<eps then exit(0)
      else if t<0 then exit(-1)
      else exit(1);
    end;
function lower2(p1,p2:point):boolean;
    var
      a1,a2,b1,b2,t:double;
    begin
      a1:=p1.x-a[0].x;
      b1:=p1.y-a[0].y;
      a2:=p2.x-a[0].x;
      b2:=p2.y-a[0].y;
      t:=a1*b2-a2*b1;
      lower2:=false;
      if t>eps then lower2:=true
      else if (abs(t)<eps) then exit(p1.x<p2.x);
    end;
function lower(p1,p2:point):boolean;
    var
      a1,a2,b1,b2,t:double;
    begin
      a1:=p1.x-a[1].x;
      b1:=p1.y-a[1].y;
      a2:=p2.x-a[1].x;
      b2:=p2.y-a[1].y;
      t:=a1*b2-a2*b1;
      lower:=false;
      if t>eps then lower:=true
      else if (abs(t)<eps) then lower:=lower2(p1,p2);
    end;
procedure sort(l,r:longint);
    var
      i,j:longint;
      mid:point;
    begin
      i:=l; j:=r; mid:=a[l+random(r-l+1)];
      repeat
        while lower(a[i],mid) do inc(i);
        while lower(mid,a[j]) do dec(j);
        if i<=j then
          begin
            swap(a[i],a[j]);
            inc(i); dec(j);
          end;
      until i>j;
      if i<r then sort(i,r);
      if l<j then sort(l,j);
    end;
procedure graham;
    var
      i,c:longint;
    begin
      c:=1;
      for i:=2 to n do
        if (a[i].y<a[c].y) or ((a[i].y=a[c].y) and (a[i].x<a[c].x)) then c:=i;
      swap(a[c],a[1]);
      a[0]:=a[1]; a[0].x-=1;
      if n>2 then sort(2,n);
      i:=n; n:=2; ch[1]:=a[1]; ch[2]:=a[2];
      for i:=3 to i do
        begin
          while (n>1) and (CCW(ch[n-1],ch[n],a[i])<>1) do dec(n);
          inc(n);
          ch[n]:=a[i];
        end;
    end;
function dt(i,j,k:point):longint;
    begin
      exit(abs((j.x-i.x)*(j.y+i.y)
              +(k.x-j.x)*(k.y+j.y)
              +(i.x-k.x)*(i.y+k.y)));
    end;
procedure inp;
    var
      i:longint;
    begin
      for i:=1 to n do
        with a[i] do
          read(f1,x,y);
    end;
procedure solve;
    var
      i,j,ii,temp,best,now:longint;
    begin
      if n<3 then begin writeln(f2,'0.00'); exit; end;
      best:=dt(ch[1],ch[2],ch[3]);
      for i:=1 to n-2 do
        begin
          ii:=i+1;
          for j:=i+2 to n do
            begin
              now:=0;
              repeat
                temp:=dt(ch[ii],ch[i],ch[j]);
                if temp>=now then now:=temp
                else break;
                inc(ii); if ii>j then break;
              until false;
              dec(ii); best:=max(best,now);
            end; //for j
        end; //for i
      for i:=1 to n-2 do
        begin
          ii:=i+3;
          for j:=i+2 to n-1 do
            begin
              now:=0;
              repeat
                temp:=dt(ch[ii],ch[i],ch[j]);
                if temp>=now then now:=temp
                else break;
                inc(ii); if ii>n then break;
              until false;
              dec(ii); best:=max(best,now);
            end;
        end; //for i
      writeln(f2,best/2:0:2);
    end;
procedure duyet;
    var
      i,j,k,li,lj,lk,best:longint;
    begin
      best:=0;
      for i:=1 to n do
      for j:=1 to n do
      for k:=1 to n do
        if dt(a[i],a[j],a[k])>best then
          begin
            best:=dt(a[i],a[j],a[k]);
            li:=i; lj:=j; lk:=k;
          end;
      writeln(f2,best/2:0:2,' ',li,' ',lj,' ',lk);
    end;

var
  test:longint;
begin
  openF;
  read(f1,n);
  test:=0;
  while (n>0) do
    begin
      inc(test);
      inp;
      graham;
      solve;
      read(f1,n);
    end;
  closeF;
end.

Code mẫu của hieult

#include<cstdio>
#include<cmath>
#include<cstring>
#include<cstdlib>
#include<cassert>
#include<ctime>
#include<algorithm>
#include<iterator>
#include<iostream>
#include<cctype>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<list>
//#include<conio.h>
#define oo 1111111111
#define nmax 100111
#define MAX 222

using namespace std;

struct point{
     int x,y;
     bool operator == (point D) const{
          return (x == D.x && y == D.y);       
     }
};



point  a[nmax],b[nmax],p;
int n,m,N,test;

long long kc(point a,point b){
      long long X = (b.x-a.x);
      long long Y = (b.y-a.y);
      return X*X+Y*Y;
}

double dientich(point a,point b,point c){
      double KQ = 0.5*((a.x*1.*b.y-a.y*1.*b.x)+(b.x*1.*c.y-b.y*1.*c.x)+(c.x*1.*a.y-c.y*1.*a.x));
      return KQ>0?KQ:-KQ;
}

bool behon(point a,point b,point bn){
      long long ax,ay,bx,by;
      ax = a.x - bn.x;
      ay = a.y - bn.y;
      bx = b.x - bn.x;
      by = b.y - bn.y;
      if(ay!=0 && by==0) return true;
      if(ay==0||by==0) return false;
      return ax*by>ay*bx;
}

void Sort(point a[],int l,int r){
      int i = l,j = r;
      point mid = a[(l+r)/2];
      while(i<j){
           while(behon(a[i],mid,a[0])) i++;
           while(behon(mid,a[j],a[0])) j--;
           if(i<=j) swap(a[i++],a[j--]);
      }
      if(i<r) Sort(a,i,r);
      if(l<j) Sort(a,l,j);
}

int ccw(point p1,point p2,point p3){
      long long a1,a2,b1,b2,t;
      a1 = p2.x-p1.x;
      a2 = p3.x-p1.x;
      b1 = p2.y-p1.y;
      b2 = p3.y-p1.y;
      t = a1*b2-a2*b1;
      if(t==0) return 0;
      if(t>0) return 1;
      return -1;
}

int graham(point a[],int n){
      int m = 1;
      for(int i = 2;i<=n;i++)
           if(a[m].y>a[i].y) m = i;
      for(int i = 1;i<=n;i++)
           if(a[i].y==a[m].y && a[i].x>a[m].x) 
                m = i;
      swap(a[1],a[m]);
      a[0].x = a[1].x;
      a[0].y = a[1].y-1;
      Sort(a,2,n);
      a[++n] = a[1];
      m = 2;
      bool ok = true;
      for(int i = 3;i<=n;i++){
             ok = true;
             while(ccw(a[m],a[m-1],a[i])>=0){
                   if(ccw(a[m],a[m-1],a[1])==0){
                        ok = false;
                        if(kc(a[m],a[m-1])<kc(a[m-1],a[i]))
                              swap(a[m],a[i]);
                        break;      
                   }
                   else m--;    
             }
             if(ok) swap(a[++m],a[i]);
      }
      return --m;  
} 

long long stg(point a,point b,point c){
     long long s = (b.x-a.x)*1LL*(b.y+a.y)+(c.x-b.x)*1LL*(c.y+b.y)+ (a.x-c.x)*1LL*(a.y+c.y);
     return s>0?s:-s; 
}

int thuoc(point a,point b,point c){
               if(ccw(a,b,c)==0 && ((a.y<=c.y && c.y<=b.y)||(a.y>=c.y && c.y>=b.y))) return true;
               else return false;

}

int namtrong(point p,int l,int r,point b[]){
     while(r-l>2){
          int mid = (l+r+1)/2;
          int k = ccw(b[1],b[mid],p);
          if(k==0){
                if((b[1].x-p.x)*(b[mid].x-p.x)<0) return 1;;
                return 0;
          }
          if(k==1) l = mid-1;
          if(k==-1) r = mid;
     }
     point x,y,z;
     x = b[1];
     y = b[r];
     z = b[r-1];
     long long k = stg(x,y,z);
     long long t = stg(x,y,p)+stg(x,z,p)+stg(y,z,p);
     if(t>k) return 0;
     int kk = ccw(x,y,p)*ccw(x,z,p)*ccw(y,z,p);
     if(kk!=0) return 1;
     if(p==x||p==y||p==z) return 0;
     if(r==3){
           if(n<=3) return 0;
           if(ccw(x,y,p)==0)
                 return 1;
     }
     if(r==n &&ccw(x,z,p)==0)
          return 1;
     if(ccw(x,y,p)==0 && r!=n)
           return 1;
     if(ccw(x,z,p)==0 && r!=3)
           return 1;
     return 0;
}

int main(){

    // freopen("input.in","r",stdin);
    // freopen("output.out","w",stdout);

     while(scanf("%d",&n)>0 && n>0){
          for(int i = 1;i<=n;i++) scanf("%d %d",&a[i].x,&a[i].y);
          n = graham(a,n);
          for(int i = n + 1; i <= 2 * n; i++){
               a[i] = a[i - n];  
          }
          double kq = 0;
        //  printf("%d\n",n);

          for(int i = 1;i<=n;i++){
               int u = i + 1;
               for(int j = i + 1;j<=n;j++){
                    while(dientich(a[i],a[j],a[u + 1]) > dientich(a[i], a[j], a[u]) && u < n) u++;
                 //   printf("%d %d %d\n",i,j,u);
                    kq = max(kq, dientich(a[i], a[j], a[u]));
               }

          } 
          printf("%.2lf\n",kq);
     }
     //getch();

}

Code mẫu của ll931110

#include <algorithm>
#include <bitset>
#include <cmath>
#include <ctime>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <iostream>
#include <map>
#include <set>
#include <sstream>
#include <stack>
#include <queue>
#include <utility>
#include <vector>
using namespace std;

vector< pair<int,int> > point;
int n;

int cross_product(pair<int,int> A,pair<int,int> B,pair<int,int> C)
{
    int xa = B.first - A.first,ya = B.second - A.second;
    int xb = C.first - B.first,yb = C.second - B.second;
    return xa * yb - xb * ya;
}

int area(pair<int,int> A,pair<int,int> B,pair<int,int> C)
{
    return abs(cross_product(A,B,C));
}

vector< pair<int,int> > convex_hull(vector< pair<int,int> > v)
{
  if (n < 3) return v;
  sort(v.begin(),v.end());
  pair<int,int> p1 = v[0],p2 = v[n - 1];

  vector< pair<int,int> > up,down;
  up.push_back(p1);  down.push_back(p1);
  for (int i = 1; i < n; i++)
  {
      int cross = cross_product(p1,v[i],p2);
      if (i == n - 1 || cross > 0)
      {
        while (down.size() > 1 && cross_product(down[down.size() - 2],down[down.size() - 1],v[i]) <= 0) down.pop_back();
        down.push_back(v[i]);        
      }
      if (i == n - 1 || cross < 0)
      {
        while (up.size() > 1 && cross_product(up[up.size() - 2],up[up.size() - 1],v[i]) >= 0) up.pop_back();
        up.push_back(v[i]);
      }
  }
  for (int i = up.size() - 2; i > 0; i--) down.push_back(up[i]);
  return down;
}

int optimal(vector< pair<int,int> > v)
{
    n = v.size();
    if (n < 3) return 0;

    int a = 0,b = 1,c = 2,ret = area(v[0],v[1],v[2]);
    while (1)
    {
      while (1)
      {
        int _c = c + 1;  if (_c >= n) _c = 0;
        if (area(v[a],v[b],v[_c]) > area(v[a],v[b],v[c]))
        {
          ret = max(ret,area(v[a],v[b],v[_c]));  c = _c;
        }
        else break;
      }
      while (1)
      {
        int _b = b + 1;  if (_b >= n) _b = 0;
        if (area(v[a],v[_b],v[c]) > area(v[a],v[b],v[c]))
        {
          ret = max(ret,area(v[a],v[_b],v[c]));  b = _b;
        }
        else break;
      }
      bool flag = false;
      while (1)
      {
        int _a = a + 1;  if (_a >= n) _a = 0;
        if (area(v[_a],v[b],v[c]) > area(v[a],v[b],v[c]))
        {
          flag = true;  ret = max(ret,area(v[_a],v[b],v[c]));  a = _a;
        }
        else break;
      }
      if (!flag)
      {
        a++;  if (a >= n) a = 0;
        if (a == b)
        {
          b++;  if (b >= n) b = 0;
        }
        if (b == c)
        {
          c++;  if (c >= n) c = 0;
        }
      }
      if (a == 0) break;
    }
    return ret;
}

int main()
{
//    freopen("mtriarea.in","r",stdin);
//    freopen("mtriarea.ou","w",stdout);
    while (1)
    {
      scanf("%d", &n);  if (n < 0) return 0;
      point.resize(n);
      for (int i = 0; i < n; i++) scanf("%d %d", &point[i].first, &point[i].second);
      point = convex_hull(point);
      printf("%.2lf\n", optimal(point)/2.0);
    }
}