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 <iostream>
#include <algorithm>
#include <vector>
using namespace std;

typedef double D;
const D EPS = 1e-8;

struct P {
  D x, y;
  P() { }
  P(D x_, D y_) : x(x_), y(y_) { }
};

P operator +(P a, P b) { return P(a.x + b.x, a.y + b.y); }
P operator -(P a, P b) { return P(a.x - b.x, a.y - b.y); }
P operator *(P a, D b) { return P(a.x * b, a.y * b); }
P operator /(P a, D b) { return P(a.x / b, a.y / b); }
P vec(P from, P to) { return to - from; }
D inp(P a, P b) { return a.x*b.x + a.y*b.y; }
D outp(P a, P b) { return a.x*b.y - a.y*b.x; }
D norm(P p) { return inp(p, p); }

int sig(D a, D b) {
  if(a < b - EPS) return -1;
  if(a > b + EPS) return +1;
  return 0;
}

int ccw(P a, P b, P c) { // 重なっている点があるとうまく動かないと思われる
  b = vec(a, b); c = vec(a, c);

  // a - b - c が折れ曲がるとき
  if(sig(outp(b, c),0.0) > 0) return +1; // 反時計回り
  if(sig(outp(b, c),0.0) < 0) return -1; // 時計回り

  // a - b - c が直線上に並ぶとき
  // sigを使わない実装が主流っぽい？
  if(sig(inp(b, c),0.0) < 0)   return +2; // c - a - b
  if(sig(norm(b),norm(c)) < 0) return -2; // a - b - c
  return 0;                               // a - c - b
}

// ON = 0, IN = 1, OUT = -1
int containsGP(vector<P> g, P p) {
  int side = -1;
  for(int i = 0; i < (int)g.size(); i++) {
    if(ccw(g[i], g[(i+1)%g.size()], p) == 0) return 0;
    P a = vec(p, g[i]);
    P b = vec(p, g[(i+1)%g.size()]);
    if(a.y > b.y) swap(a, b);
    if(sig(a.y, 0.0) <= 0 && sig(b.y, 0.0) > 0 && sig(outp(a, b), 0.0) > 0) side *= -1;
  }
  return side;
}

int main() {
  int N; cin >> N;
  while(N--) {
    vector<P> tri(3);
    for(int i = 0; i < 3; ++i) {
      cin >> tri[i].x >> tri[i].y;
    }
    P k, s;
    cin >> k.x >> k.y;
    cin >> s.x >> s.y;
    int side = containsGP(tri, k);
    side *= containsGP(tri, s);
    cout << (side == -1 ? "OK" : "NG") << endl;
  }
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <cassert>
#include <iostream>
#include <cctype>
#include <sstream>
#include <string>
#include <list>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <map>
#include <utility>
#include <numeric>
#include <algorithm>
#include <iterator>
#include <bitset>
#include <complex>
#include <fstream>
using namespace std;
typedef long long ll;
const double EPS = 1e-5;
typedef vector<int> vint;
typedef pair<int, int> pint;
#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for(int i = x; i < n; i++)
template<class T> T RoundOff(T a){ return int(a+.5-(a<0)); }
template<class T, class C> void chmax(T& a, C b){ if(a < b) a = b; }
template<class T, class C> void chmin(T& a, C b){ if(b < a) a = b; }
template<class T, class C> pair<T, C> mp(T a, C b){ return make_pair(a, b); }

typedef complex<double> P;

// OÏ
double cross(P a, P b)
{	return a.real() * b.imag() - b.real() * a.imag();	}

// àÏ
double dot(P a, P b)
{	return a.real() * b.real() + a.imag() * b.imag();	}

// _ÆüªÌ£
double dist(P a, P b, P c)
{
	if(dot(b - a, c - a) < EPS) return abs(c - a);
	if(dot(a - b, c - b) < EPS) return abs(c - b);
	
	return abs(cross(b - a, c - a)) / abs(b - a);
}

// _ªOp`ÌÉ é©
bool isInTriangle(P p[3], P x)
{
	double S = abs(p[0] - p[1]) * dist(p[0] ,p[1], p[2]);
	
	rep(i, 3) S -= abs(p[i] - p[(i + 1) % 3]) * dist(p[i], p[(i + 1) % 3], x);
	
	return abs(S) < EPS;
}

int main()
{
    int n;
	cin >> n;
	
	
	while(n--)
	{
		P p[3];
		P k, s;
		
		rep(i, 3) cin >> p[i].real() >> p[i].imag();
		cin >> k.real() >> k.imag() >> s.real() >> s.imag();
	
		if(isInTriangle(p, k) ^ isInTriangle(p, s))
		{
			cout << "OK" << endl;
		}
		else
		{
			cout << "NG" << endl;
		}
	}
}

C++: #include <iostream>
#include <cmath>
#include <cstdio>

using namespace std;

typedef double D; 
#define EPS (1e-6)
#define equal(a,b) (fabs((a)-(b)) < EPS)

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

struct Point{
  D x,y;

  Point (D x = 0, D y = 0) : 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 * (D a) {
    return Point( a*x , a*y );
  }
  
  D norm() {
    return x*x+y*y;
  }

  D dot(Point p){
    return add(x*p.x , y*p.y);
  }

  D det(Point p){
    return add(x*p.y , -y*p.x);
  }  
};

int ccw(Point p0,Point p1,Point p2){
  Point a = p1 - p0;
  Point b = p2 - p0;

  if(a.det(b) > EPS) return 1;
  if(a.det(b) < -EPS) return -1;
  if(a.dot(b) < -EPS) return 2;
  if(a.norm() < b.norm()) return -2;
  return 0;
}

D S(Point p1,Point p2,Point p3){
  D a = sqrt(pow(p1.x-p2.x,2) + pow(p1.y-p2.y,2));
  D b = sqrt(pow(p1.x-p3.x,2) + pow(p1.y-p3.y,2));
  D c = sqrt(pow(p3.x-p2.x,2) + pow(p3.y-p2.y,2));
  D s = (a + b + c) / 2;

  return sqrt(s*(s - a)*(s - b)*(s - c));
}

bool check(Point p1,Point p2,Point p3,Point p4){
  return (ccw(p1,p2,p3)*ccw(p1,p2,p4) < 0 &&
	  ccw(p3,p4,p1)*ccw(p3,p4,p2) < 0);
}

bool eq(D S1,D S2){
  return equal(S1,S2);
}

int main(){
  int n;
  Point P[3],T[2];

  cin >> n;
  while(n--){
    scanf("%lf %lf" ,&P[0].x ,&P[0].y);
    scanf("%lf %lf" ,&P[1].x ,&P[1].y);
    scanf("%lf %lf" ,&P[2].x ,&P[2].y);
    scanf("%lf %lf" ,&T[0].x ,&T[0].y);
    scanf("%lf %lf" ,&T[1].x ,&T[1].y);

    bool ok = false;
    D S1 = S(P[0],P[1],P[2]);
    D S2 = S(P[0],P[1],T[0])+S(P[0],P[2],T[0])+S(P[1],P[2],T[0]);
    D S3 = S(P[0],P[1],T[1])+S(P[0],P[2],T[1])+S(P[1],P[2],T[1]);

    if(eq(S1,S2) && eq(S1,S3)){
      puts("NG");
      continue;
    }

    if(!eq(S1,S2) && !eq(S1,S3)){
      puts("NG");
      continue;
    }

    if(!eq(S1,S3)){
      puts("NG");
      continue;
    }

    if(check(P[0],P[1],T[0],T[1])){
      ok = true;
    }    
    if(check(P[0],P[2],T[0],T[1])){
      ok = true;
    }  
    if(check(P[1],P[2],T[0],T[1])){
      ok = true;
    }  

    if(ok){
      puts("OK");
    }else{
      puts("NG");
    }
  }

  return 0;
}