解法一：中序遍历+后续遍历+BFS

根据后序遍历找出根结点，结合中序遍历划分左右子树，推理出整棵树的结构。再进行BFS。

import java.io.*;
import java.util.*;
public class Main {
    // 后序遍历
    private static int[] postOrder;
    // 中序遍历
    private static int[] inOrder;
    public static void main(String[] args) throws IOException {
        StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        in.nextToken();
        int N = (int) in.nval;
        postOrder = new int[N];
        for (int i = 0; i < N; ++i) {
            in.nextToken();
            postOrder[i] = (int) in.nval;
        }
        inOrder = new int[N];
        for (int i = 0; i < N; ++i) {
            in.nextToken();
            inOrder[i] = (int) in.nval;
        }
        TreeNode root = build(0, N - 1, 0, N - 1);
        levelOrder(N, root, out);
    }
    private static TreeNode build(int postL, int postR, int inL, int inR) {
        if (postL > postR || inL > inR) {
            return null;
        }
        int val = postOrder[postR];
        TreeNode root = new TreeNode(val);
        int index = inL;
        for (; (inOrder[index] != val) && (index <= inR); ++index) ;
        int leftLen = index - inL;
        root.left = build(postL, postL + leftLen - 1, inL, index - 1);
        root.right = build(postL + leftLen, postR - 1, index + 1, inR);
        return root;
    }
    private static void levelOrder(int N, TreeNode root, PrintWriter out) {
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; ++i) {
                TreeNode tmp = queue.poll();
                if (tmp==root) {
                    out.print(tmp.val);
                }else {
                    out.print(" " + tmp.val);
                }
                if (tmp.left != null) {
                    queue.offer(tmp.left);
                }
                if (tmp.right != null) {
                    queue.offer(tmp.right);
                }
            }
        }
        out.println();
        out.flush();
    }
}
class TreeNode {
    TreeNode left;
    TreeNode right;
    int val;
    public TreeNode(int val) {
        left = null;
        right = null;
        this.val = val;
    }
}