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 <stdio.h>
#include <iostream>
#include <vector>
#include <list>
#include <cmath>
#include <fstream>
#include <algorithm>
#include <string>
#include <queue>
#include <set>
#include <map>
#include <complex>
#include <iterator>
#include <cstdlib>
#include <cstring>
#include <sstream>

using namespace std;

#define EPS (1e-10)
#define EQ(a,b) (abs((a) - (b)) < EPS)
#define EQV(a,b) (EQ((a).real(),(b).real()) && EQ((a).imag(),(b).imag()))

typedef complex<double> P;
typedef long long ll;

const int MAX_SIZE = 10000;

// àÏ
double dot(P a, P b) {
  return (a.real() * b.real() + a.imag() * b.imag());
}
// OÏ
double cross(P a, P b) {
  return (a.real() * b.imag() - a.imag() * b.real());
}
// _cª¼üabãÉ é©È¢©
int is_point_on_line(P a, P b, P c) {
  return EQ( cross(b-a, c-a), 0.0 );
}
// 2¼üÌ¼s»è
int is_orthogonal(P a1, P a2, P b1, P b2) {
  return EQ( dot(a1-a2, b1-b2), 0.0 );
}
// 2¼üÌ½s»è
int is_parallel(P a1, P a2, P b1, P b2) {
  return EQ( cross(a1-a2, b1-b2), 0.0 );
}
// _a,bðÊé¼üÆ_cÌÔÌ£
double distance_l_p(P a, P b, P c) {
  return abs(cross(b-a, c-a)) / abs(b-a);
}
// _a,bð[_Æ·éüªÆ_cÆÌ£
double distance_ls_p(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);
}
// a1,a2ð[_Æ·éüªÆb1,b2ð[_Æ·éüªÌð·»è
int is_intersected_ls(P a1, P a2, P b1, P b2) {
  return ( cross(a2-a1, b1-a1) * cross(a2-a1, b2-a1) < EPS ) &&
         ( cross(b2-b1, a1-b1) * cross(b2-b1, a2-b1) < EPS );
}
// a1,a2ð[_Æ·éüªÆb1,b2ð[_Æ·éüªÌð_vZ
P intersection_ls(P a1, P a2, P b1, P b2) {
  P b = b2-b1;
  double d1 = abs(cross(b, a1-b1));
  double d2 = abs(cross(b, a2-b1));
  double t = d1 / (d1 + d2);

  return a1 + (a2-a1) * t;
}
// a1,a2ðÊé¼üÆb1,b2ðÊé¼üÌð·»è
int is_intersected_l(P a1, P a2, P b1, P b2) {
  return !EQ( cross(a1-a2, b1-b2), 0.0 );
}
// a1,a2ðÊé¼üÆb1,b2ðÊé¼üÌð_vZ
P intersection_l(P a1, P a2, P b1, P b2) {
  P a = a2 - a1; P b = b2 - b1;
  return a1 + a * cross(b, b1-a1) / cross(b, a);
}
/*
~üÆüªÌð·»è
*/
bool isCircleCrossLine(P a,P b,P c,double r){
	double d1 = abs(a-c);
	double d2 = abs(b-c);
	if(d1<r&&d2<r){
		return false;
	}
	double d = distance_ls_p(a,b,c);
	if(EQ(d,r)||d<r){
		return true;
	}
	else
		return false;
}
// Op`ÌàÉ_ª é©Ç¤©
// OÏÌÏªÈçàÉ_ è
bool isInTriangle(P p1,P p2,P p3,P s){
	P a=p1-s;
	P b=p2-s;
	P c=p3-s;
	return (cross(a,b)*cross(b,c)*cross(c,a)>=0);
}

int main(){

	int n;
	cin>>n;
	for(int i = 0; i < n; i++){
		int xp1,yp1,xp2,yp2,xp3,yp3,xk,yk,xs,ys;
		cin>>xp1>>yp1>>xp2>>yp2>>xp3>>yp3>>xk>>yk>>xs>>ys;
		P p1(xp1,yp1);
		P p2(xp2,yp2);
		P p3(xp3,yp3);
		P k(xk,yk);
		P s(xs,ys);
		// ¼ûÆàOp`ÌàÉ_ª éê
		if(isInTriangle(p1,p2,p3,k)&&isInTriangle(p1,p2,p3,s)){
			cout<<"NG"<<endl;
		}
		// ¼ûÆàOp`ÌOÉ_ª éê
		else if(!isInTriangle(p1,p2,p3,k)&&!isInTriangle(p1,p2,p3,s)){
			cout<<"NG"<<endl;
		}
		else
			cout<<"OK"<<endl;
	}

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
bool line(int x1, int y1, int x2, int y2, int x, int y){
    return (x2 - x1) * (y - y1) > (y2 - y1) * (x - x1);
}

bool triangle(int x1, int y1, int x2, int y2, int x3, int y3, int x, int y){
    return  line(x1, y1, x2, y2, x, y) == line(x1, y1, x2, y2, x3, y3) &&
            line(x2, y2, x3, y3, x, y) == line(x2, y2, x3, y3, x1, y1) &&
            line(x3, y3, x1, y1, x, y) == line(x3, y3, x1, y1, x2, y2);
}

int main(){
    int n;
    scanf("%d", &n);
    for(int i = 0; i < n; ++i){
        int x1, y1, x2, y2, x3, y3, ax, ay, bx, by;
        scanf("%d%d%d%d%d%d%d%d%d%d", &x1, &y1, &x2, &y2, &x3, &y3, &ax, &ay, &bx, &by);
        if(triangle(x1, y1, x2, y2, x3, y3, ax, ay) != triangle(x1, y1, x2, y2, x3, y3, bx, by)){
            printf("OK\n");
        }
        else{
            printf("NG\n");
        }
    }
    return 0;
}