241101 맹독 방벽

static class Point {
	int x;
	int y;

	Point(int x, int y) {
		this.x = x;
		this.y = y;
	}
}

static int n;
static int l;
static Point[] arr;
static Point[] newPoints;

public static void main(String[] args) throws Exception {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	StringTokenizer token = new StringTokenizer(br.readLine());
	n = Integer.parseInt(token.nextToken());
	l = Integer.parseInt(token.nextToken());

	arr = new Point[n + 1];

	for (int i = 0; i < n; i++) {
		token = new StringTokenizer(br.readLine());
		int x = Integer.parseInt(token.nextToken());
		int y = Integer.parseInt(token.nextToken());

		arr[i] = new Point(x, y);
	}

	int minIndex = 0;

	for (int i = 1; i < n; i++) {
		if (arr[i].y < arr[minIndex].y) {
			minIndex = i;
		} else if (arr[i].y == arr[minIndex].y) {
			if (arr[i].x < arr[minIndex].x) {
				minIndex = i;
			}
		}
	}

	Point temp = arr[0];
	arr[0] = arr[minIndex];
	arr[minIndex] = temp;

	Arrays.sort(arr, 1, n, new Comparator<Point>() {
		@Override
		public int compare(Point p1, Point p2) {
			int c = ccw(arr[0], p1, p2);
			if (c == 0) {
				return dist(arr[0], p2) >= dist(arr[0], p1) ? -1 : 1;
			}
			return c;
		}
	});

	newPoints = new Point[n + 1];
	newPoints[0] = arr[n - 1];

	for (int i = 1; i <= n; i++) {
		newPoints[i] = arr[i - 1];
	}

	int m = 1;

	for (int i = 2; i <= n; i++) {
		while (ccw(newPoints[m - 1], newPoints[m], newPoints[i]) >= 0) {
			if (m > 1) {
				m -= 1;
			} else if (i == n)
				break;
			else
				i += 1;
		}

		m += 1;

		Point tmp = newPoints[m];
		newPoints[m] = newPoints[i];
		newPoints[i] = tmp;
	}

	double ans = 0;

	for (int i = 0; i < m; i++) {
		ans += getDistance(newPoints[i], newPoints[i + 1]);
	}
	ans += (2 * l * Math.PI);

	System.out.println(Math.round(ans));
}

static long dist(Point p1, Point p2) {
	return ((long) p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y);
}

static double getDistance(Point p1, Point p2) {
	return Math.sqrt(dist(p1, p2));
}

static int ccw(Point p1, Point p2, Point p3) {
	long temp = ((long) p1.x * p2.y) + (p2.x * p3.y) + (p3.x * p1.y);
	temp -= (p1.y * p2.x) + (p2.y * p3.x) + (p3.y * p1.x);

	if (temp > 0) {
		return -1;
	} else if (temp < 0) {
		return 1;
	} else {
		return 0;
	}
}

출처:https://www.acmicpc.net/problem/7420