Go: package main

import (
	"bufio"
	"os"
	"strconv"
	"strings"
	"fmt"
)

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	scanner.Scan()
	n, _ := strconv.Atoi(scanner.Text())
	for i := 0; i < n; i++ {
		scanner.Scan()
		input := strings.Split(scanner.Text(), " ")
		buf := make([]float64, len(input))
		for j := range buf {
			buf[j], _ = strconv.ParseFloat(input[j], 64)
		}
		p1 := complex(buf[0], buf[1])
		p2 := complex(buf[2], buf[3])
		p3 := complex(buf[4], buf[5])
		pk := complex(buf[6], buf[7])
		ps := complex(buf[8], buf[9])
		kin := isAtSameSide(p3, pk, []complex128{p1, p2}) &&
			isAtSameSide(p1, pk, []complex128{p2, p3}) &&
			isAtSameSide(p2, pk, []complex128{p3, p1})
		sin := isAtSameSide(p3, ps, []complex128{p1, p2}) &&
			isAtSameSide(p1, ps, []complex128{p2, p3}) &&
			isAtSameSide(p2, ps, []complex128{p3, p1})
		if (kin || sin) && !(kin && sin) {
			fmt.Println("OK")
		} else {
			fmt.Println("NG")
		}
	}
}

func isAtSameSide(a, b complex128, line []complex128) bool {
	sa := (real(line[1]) - real(line[0]))*(imag(a)-imag(line[0]))+
		(imag(line[1])-imag(line[0]))*(real(line[0])-real(a))
	sb := (real(line[1]) - real(line[0]))*(imag(b)-imag(line[0]))+
		(imag(line[1])-imag(line[0]))*(real(line[0])-real(b))
	return (sa > 0 && sb > 0) || (sa < 0 && sb < 0)
}

C++: #include<cmath>
#include<algorithm>
#include<iostream>
#include<vector>
#include<climits>
#include<cfloat>
 
using namespace std;
 
double EPS = 1e-10;
 
double add(double a, double b){
  if(abs(a+b) < EPS * (abs(a)+abs(b)))return 0;
  return a+b;
}
 
struct point{
  double x, y;
  point(){}
  point(double x,double y) : x(x) , y(y){}

  point operator + (point p){
    return point(add(x,p.x), add(y,p.y));
  }
 
  point operator - (point p){
    return point(add(x,-p.x), add(y,-p.y));
  }
 
  point operator * (double d){
    return point(x*d,y*d);
  }
};
 
struct segment{
  point a,b;
};
 
double dot(point a, point b) {
  return (a.x * b.x + a.y * b.y);
}
 
double cross(point a, point b) {
  return (a.x * b.y - a.y * b.x);
}
 
int is_intersected_ls(point a1, point a2, point b1, point b2) {
  return ( cross(a2-a1, b1-a1) * cross(a2-a1, b2-a1) < EPS ) &&
         ( cross(b2-b1, a1-b1) * cross(b2-b1, a2-b1) < EPS );
}

int is_point_on_line(point a, point b, point c) {
  return cross(b-a, c-a)==0.0 &&
         (dot(b-a, c-a) > -EPS) &&
         (dot(a-b, c-b) > -EPS);
}

int inside(point p, vector<point> ps){
  point a(p.x,p.y),b(1000000,p.y);

  double ymx=-DBL_MAX,ymn=DBL_MAX;
  for(int i=0;i<ps.size();i++){
    ymx=max(ymx,ps[i].y);
    ymn=min(ymn,ps[i].y);
  }
  if(a.y<=ymn||a.y>=ymx)return 0;

  int cnt1=0;
  for(int i=0;i<ps.size();i++)
    if(is_point_on_line(a,b,ps[i]))cnt1++;
  
  int cnt=0;
  for(int i=0;i<ps.size();i++)
    if(is_intersected_ls(ps[i],ps[(i+1)%ps.size()],a,b))cnt++;

  return (cnt-cnt1)%2;
}

int main(void){
  int n;
  point k,s,in;
  vector<point>p; 

  cin >> n;
  while(n--){
    p.clear();
    for(int i=0;i<3;i++){
      cin >> in.x >> in.y;
      p.push_back(in);
    }     

    cin >> k.x >> k.y >> s.x >> s.y;

    if(inside(k,p)!=inside(s,p))cout << "OK" << endl;
    else cout << "NG" << endl;
     
  }
 
  return 0;
}

C++: #include<cmath>
#include<algorithm>
#include<iostream>
#include<vector>

using namespace std;

double EPS = 1e-10;

double add(double a, double b){
  if(abs(a+b) < EPS * (abs(a)+abs(b)))return 0;
  return a+b;
}

struct point{
  double x, y;
  point(){}
  point(double x,double y) : x(x) , y(y){}

  point operator + (point p){
    return point(add(x,p.x), add(y,p.y));
  }

  point operator - (point p){
    return point(add(x,-p.x), add(y,-p.y));
  }

  point operator * (double d){
    return point(x*d,y*d);
  }
};

struct segment{
  point a,b;
};

double dot(point a, point b) {
  return (a.x * b.x + a.y * b.y);
}

double cross(point a, point b) {
  return (a.x * b.y - a.y * b.x);
}

int is_intersected_ls(point a1, point a2, point b1, point b2) {
  return ( cross(a2-a1, b1-a1) * cross(a2-a1, b2-a1) < EPS ) &&
         ( cross(b2-b1, a1-b1) * cross(b2-b1, a2-b1) < EPS );
}

int ccw(point p0, point p1, point p2){
  point a = p1 - p0;
  point b = p2 - p0;
  if(cross(a,b)>EPS)return +1;
  if(cross(a,b)<EPS)return -1;
  if(dot(a,b)<-EPS)return +2;
  if(a.x*a.x+a.y*a.y<b.x*b.x+b.y*b.y)return -2;
  return 0;
}


//時計回りに辺を構築する。
vector<segment> construct_edge(point* p, int n){
  vector<segment>seg,seg2;
  segment temp;

  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      if(i!=j){
	temp.a=p[i];
	temp.b=p[j];
	seg.push_back(temp);
      }
    }
  }

  int t=seg.size();
  for(int i=0;i<t;i++){
    int fg=0;
    for(int j=0;j<t;j++){
      if(i!=j && seg[i].b.x==seg[j].a.x && seg[i].b.y==seg[j].a.y){
	if(ccw(seg[i].a,seg[i].b,seg[j].b)==1){
	  fg=1;
	  break;
	}
      }
    }
    if(!fg)seg2.push_back(seg[i]);
  }
  return seg2;
}
/*
点と多角形の内外判定

ps 多角形の辺
p  点
n  多角形の辺の数

点が多角形に含まれれば1,
そうでなければ0を返す。
*/
int point_contain(vector<segment> ps, point p, int n){
  point q;
  q.x=100000000;
  q.y=p.y;
  int cnt=0;
  for(int i=0;i<n;i++){
    if(ps[i].a.y==p.y || ps[i].b.y ==p.y)cnt+=2;
    else cnt+=is_intersected_ls(ps[i].a,ps[i].b,p,q);
  }
  return cnt%2;
}

int main(void){
  int n;
  point p[3],k,s;
  vector<segment>seg;

  cin >> n;
  while(n--){
    for(int i=0;i<3;i++)
      cin >> p[i].x >> p[i].y;
    
    cin >> k.x >> k.y >> s.x >> s.y;

    seg=construct_edge(p,3);

    if(point_contain(seg,k,3)!=point_contain(seg,s,3))cout << "OK" << endl;
    else cout << "NG" << endl;
    
  }

  return 0;
}

C++: #include <iostream>
#include <sstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <climits>
#include <cfloat>
using namespace std;

class Point
{
public:
    int y, x;
    Point(){
        y = x = 0;
    }
    Point(int y0, int x0){
        y = y0;
        x = x0;
    }
    int dot(const Point& p) const{
        return y * p.y + x * p.x; // |a|*|b|*cosÆ
    }
    int cross(const Point& p) const{
        return x * p.y - y * p.x; // |a|*|b|*sinÆ
    }
    Point operator+(const Point& p) const{
        return Point(y + p.y, x + p.x);
    }
    Point operator-(const Point& p) const{
        return Point(y - p.y, x - p.x);
    }
};

/***************************************************************************************************/
// _ªÊ½p`Ìà(ÓãàÜÞ)É é©²×é
// cp : Ê½p`
// p  : _
/***************************************************************************************************/
bool convexContain(const vector<Point>& cp, const Point& p)
{
    int n = cp.size();
    bool ret1 = true;
    bool ret2 = true;
    for(int i=0; i<n; ++i){
        int a = (cp[(i+1)%n] - cp[i]).cross(p - cp[i]);
        if(a < 0)
            ret1 = false;
        if(a > 0)
            ret2 = false;
    }
    return ret1 || ret2;
}

int main()
{
    int n;
    cin >> n;

    while(--n >= 0){
        vector<Point> cp(3);
        Point a, b;
        for(int i=0; i<3; ++i)
            cin >> cp[i].x >> cp[i].y;
        cin >> a.x >> a.y >> b.x >> b.y;

        if(convexContain(cp, a) ^ convexContain(cp, b))
            cout << "OK" << endl;
        else
            cout << "NG" << endl;
    }
}