230731 표 병합

private int[] parent = new int[2501];
private String[] value = new String[2501];

private int find(int a) {
	if (parent[a] == a)
		return a;
	else
		return parent[a] = find(parent[a]);
}

private void union(int a, int b) {
	a = find(a);
	b = find(b);
	if (a != b)
		parent[b] = a;
}

private int convertNum(int x, int y) {
	return 50 * (x - 1) + y;
}

public String[] solution(String[] commands) {
	for (int i = 1; i <= 2500; i++) {
		parent[i] = i;
		value[i] = "";
	}

	List<String> result = new ArrayList<>();
	for (String command : commands) {
		StringTokenizer st = new StringTokenizer(command);
		String cmd = st.nextToken();
		switch (cmd) {
			case "UPDATE":
				if (st.countTokens() == 2) {
					String before = st.nextToken();
					String after = st.nextToken();
					for (int i = 1; i <= 2500; i++) {
						if (before.equals(value[i]))
							value[i] = after;
					}
				} else {
					int x = Integer.parseInt(st.nextToken());
					int y = Integer.parseInt(st.nextToken());
					String after = st.nextToken();
					int num = convertNum(x, y);
					value[find(num)] = after;
				}
				break;

			case "MERGE":
				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 n1 = convertNum(x1, y1);
				int n2 = convertNum(x2, y2);
				int root1 = find(n1);
				int root2 = find(n2);
				if (root1 == root2)
					continue;
				String rootString = value[root1].isBlank() ? value[root2] : value[root1];
				value[root1] = "";
				value[root2] = "";
				union(root1, root2);
				value[root1] = rootString;
				break;

			case "UNMERGE":
				int x = Integer.parseInt(st.nextToken());
				int y = Integer.parseInt(st.nextToken());
				int num = convertNum(x, y);
				int root = find(num);
				String rootString1 = value[root];
				value[root] = "";
				value[num] = rootString1;
				List<Integer> deleteList = new ArrayList<>();
				for (int i = 1; i <= 2500; i++) {
					if (find(i) == root)
						deleteList.add(i);
				}
				for (Integer t : deleteList)
					parent[t] = t;
				break;

			case "PRINT":
				int printX = Integer.parseInt(st.nextToken());
				int printY = Integer.parseInt(st.nextToken());
				int printNum = convertNum(printX, printY);
				int printRoot = find(printNum);
				if (value[printRoot].isBlank())
					result.add("EMPTY");
				else
					result.add(value[printRoot]);
				break;
			default:
				break;

		}
	}
	return result.toArray(new String[0]);
}

출처:https://school.programmers.co.kr/learn/courses/30/lessons/150366