Java现在键盘输入一颗二叉树的先序遍历序列和中序遍历序列,试着找出它的后序遍历序列。

可以通过递归的方式来实现二叉树的构建和遍历，下面是Java代码实现：

import java.util.Scanner;

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }
}

public class BinaryTree {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入二叉树的先序遍历序列：");
        String preOrderStr = scanner.nextLine();
        System.out.print("请输入二叉树的中序遍历序列：");
        String inOrderStr = scanner.nextLine();

        int[] preOrder = new int[preOrderStr.length()];
        for (int i = 0; i < preOrderStr.length(); i++) {
            preOrder[i] = Integer.parseInt(preOrderStr.substring(i, i + 1));
        }

        int[] inOrder = new int[inOrderStr.length()];
        for (int i = 0; i < inOrderStr.length(); i++) {
            inOrder[i] = Integer.parseInt(inOrderStr.substring(i, i + 1));
        }

        TreeNode root = buildTree(preOrder, inOrder);
        System.out.print("后序遍历序列为：");
        postOrderTraversal(root);
    }

    private static TreeNode buildTree(int[] preOrder, int[] inOrder) {
        return buildTreeHelper(preOrder, 0, preOrder.length - 1, inOrder, 0, inOrder.length - 1);
    }

    private static TreeNode buildTreeHelper(int[] preOrder, int preStart, int preEnd, int[] inOrder, int inStart, int inEnd) {
        if (preStart > preEnd) {
            return null;
        }

        int rootVal = preOrder[preStart];
        TreeNode root = new TreeNode(rootVal);

        int rootIndex = 0;
        for (int i = inStart; i <= inEnd; i++) {
            if (inOrder[i] == rootVal) {
                rootIndex = i;
                break;
            }
        }

        int leftSize = rootIndex - inStart;
        root.left = buildTreeHelper(preOrder, preStart + 1, preStart + leftSize, inOrder, inStart, rootIndex - 1);
        root.right = buildTreeHelper(preOrder, preStart + leftSize + 1, preEnd, inOrder, rootIndex + 1, inEnd);

        return root;
    }

    private static void postOrderTraversal(TreeNode root) {
        if (root == null) {
            return;
        }

        postOrderTraversal(root.left);
        postOrderTraversal(root.right);
        System.out.print(root.val);
    }
}

输入格式为：

请输入二叉树的先序遍历序列：12473568
请输入二叉树的中序遍历序列：47215386

输出格式为：

后序遍历序列为：74258631

其中，`buildTree`方法用于构建二叉树，`postOrderTraversal`方法用于进行后序遍历。