Problem:
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A Point in a Triangle

There is a triangle formed by three points $(x_1, y_1)$, $(x_2, y_2)$, $(x_3, y_3)$ on a plain.

Write a program which prints "YES" if a point $P$ $(x_p, y_p)$ is in the triangle and "NO" if not.

Input

Input consists of several datasets. Each dataset consists of:

$x_1$ $y_1$ $x_2$ $y_2$ $x_3$ $y_3$ $x_p$ $y_p$

All the input are real numbers. Input ends with EOF. The number of datasets is less than or equal to 100.

Constraints

You can assume that:

$ -100 \leq x_1, y_1, x_2, y_2, x_3, y_3, x_p, y_p \leq 100$

1.0 $\leq$ Length of each side of a tringle

0.001 $\leq$ Distance between $P$ and each side of a triangle

Output

For each dataset, print "YES" or "NO" in a line.

Sample Input

0.0 0.0 2.0 0.0 2.0 2.0 1.5 0.5
0.0 0.0 1.0 4.0 5.0 3.0 -1.0 3.0

Output for the Sample Input

YES
NO

Solution in JAVA (judge verdict: Accepted)

import java.util.Scanner;

public class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		while(sc.hasNext()){
			//Initialization
			double[] a = {sc.nextDouble(), sc.nextDouble()};
			double[] b = {sc.nextDouble(), sc.nextDouble()};
			double[] c = {sc.nextDouble(), sc.nextDouble()};
			double[] p = {sc.nextDouble(), sc.nextDouble()};

			TwoVector vab, vac, vap, vca, vcb, vcp;
			vab = new TwoVector(b, a);
			vac = new TwoVector(c, a);
			vap = new TwoVector(p, a);
			vca = new TwoVector(a, c);
			vcb = new TwoVector(b, c);
			vcp = new TwoVector(p, c);

			if(TwoVector.getSgnSq(vab, vap) * TwoVector.getSgnSq(vap, vac) > 0 && TwoVector.getSgnSq(vca, vcp) * TwoVector.getSgnSq(vcp, vcb) > 0){
				System.out.println("YES");
			}else{
				System.out.println("NO");
			}
		}
	}
}
	class TwoVector{
		public double x, y;
		
		public TwoVector(double[] c){
			x = c[0];
			y = c[1];
		}
		public TwoVector(double[] c, double[] s){
			x = c[0] - s[0];
			y = c[1] - s[1];
		}

		public static double getSgnSq(TwoVector a, TwoVector b){
			return (a.x * b.y - a.y * b.x) / 2;
		}
	}