241220 트리

public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	StringBuilder sb = new StringBuilder();
	int t = Integer.parseInt(br.readLine());

	while (t-- > 0) {
		int n = Integer.parseInt(br.readLine());
		int[] preOrder = new int[n];
		int[] inOrder = new int[n];

		StringTokenizer st = new StringTokenizer(br.readLine());
		for (int i = 0; i < n; i++)
			preOrder[i] = Integer.parseInt(st.nextToken());

		st = new StringTokenizer(br.readLine());
		for (int i = 0; i < n; i++)
			inOrder[i] = Integer.parseInt(st.nextToken());

		buildPostOrder(preOrder, inOrder, 0, 0, n, sb);
		sb.append("\n");
	}

	System.out.print(sb);
}

private static void buildPostOrder(int[] preOrder, int[] inOrder, int rootIdx, int start, int end,
		StringBuilder sb) {
	if (start >= end)
		return;

	int root = preOrder[rootIdx];
	int rootPos = findRootIndex(inOrder, start, end, root);

	buildPostOrder(preOrder, inOrder, rootIdx + 1, start, rootPos, sb);
	buildPostOrder(preOrder, inOrder, rootIdx + 1 + rootPos - start, rootPos + 1, end, sb);

	sb.append(root).append(" ");
}

private static int findRootIndex(int[] inOrder, int start, int end, int root) {
	for (int i = start; i < end; i++) {
		if (inOrder[i] == root)
			return i;
	}
	return -1;
}

출처:https://www.acmicpc.net/problem/4256