241001 PIZZA ALVOLOC

public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	StringTokenizer st = new StringTokenizer(br.readLine());

	int x1 = Integer.parseInt(st.nextToken());
	int y1 = Integer.parseInt(st.nextToken());

	int x2 = Integer.parseInt(st.nextToken());
	int y2 = Integer.parseInt(st.nextToken());

	int x3 = Integer.parseInt(st.nextToken());
	int y3 = Integer.parseInt(st.nextToken());

	int x4 = Integer.parseInt(st.nextToken());
	int y4 = Integer.parseInt(st.nextToken());

	int ccw1 = computeCCW(x1, y1, x2, y2, x3, y3);
	int ccw2 = computeCCW(x1, y1, x2, y2, x4, y4);
	int ccw3 = computeCCW(x3, y3, x4, y4, x1, y1);
	int ccw4 = computeCCW(x3, y3, x4, y4, x2, y2);

	int product1 = ccw1 * ccw2;
	int product2 = ccw3 * ccw4;

	if (product1 < 0 && product2 < 0) {
		System.out.println(1);
	} else {
		System.out.println(0);
	}
	br.close();
}

private static int computeCCW(int x1, int y1, int x2, int y2, int x3, int y3) {
	int crossProduct = (x1 * y2) + (x2 * y3) + (x3 * y1)
			- (y1 * x2) - (y2 * x3) - (y3 * x1);

	if (crossProduct > 0)
		return 1;
	if (crossProduct == 0)
		return 0;
	return -1;
}

출처:https://www.acmicpc.net/problem/12781