240606 인구 이동

static int[] dr = {1, 0, -1, 0};
static int[] dc = {0, -1, 0, 1};
static int n;
static int l;
static int r;
static int[][] map;
static int[][] visitMap;
static int[] unionLand;
static int count;

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

	map = new int[n][n];
	visitMap = new int[n][n];
	unionLand = new int[n * n];
	count = 0;

	for (int i = 0; i < n; i++) {
		st = new StringTokenizer(in.readLine());
		for (int j = 0; j < n; j++) {
			map[i][j] = Integer.parseInt(st.nextToken());
			visitMap[i][j] = -1;
		}
	}

	int answer = 0;
	while (true) {
		
		int unionIndex = 0;

		if (isMoved(unionIndex, false)) {
			answer++;
		} else {
			break;
		}
		resetMap();
	}
	System.out.println(answer);
}

private static boolean isMoved(int unionIndex, boolean hasMoved) {
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			if (visitMap[i][j] == -1) {
				unionLand[unionIndex] = 0;
				searchUnion(i, j, unionIndex);
				if (count > 1) {
					hasMoved = true;
				}
				unionLand[unionIndex] /= count;
				unionIndex++;
				count = 0;
			}
		}
	}
	return hasMoved;
}

private static void searchUnion(int x, int y, int union) {
	count++;
	visitMap[x][y] = union;
	unionLand[union] += map[x][y];

	for (int i = 0; i < 4; i++) {
		int nr = x + dr[i];
		int nc = y + dc[i];
		if (!isWithinBoundary(nr, nc) || visitMap[nr][nc] != -1) {
			continue;
		}
		int diff = Math.abs(map[x][y] - map[nr][nc]);
		if (diff >= l && diff <= r) {
			searchUnion(nr, nc, union);
		}
	}
}

private static boolean isWithinBoundary(int r, int c) {
	return r >= 0 && r < n && c >= 0 && c < n;
}

private static void resetMap() {
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			map[i][j] = unionLand[visitMap[i][j]];
			visitMap[i][j] = -1;
		}
	}
}

출처:https://www.acmicpc.net/problem/16234