题解 | #二叉树遍历#递归建树，再中序递归遍历就行。

import java.util.Scanner;
public class Main {
    private static int index = 0;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            String s = sc.next();
            TreeNode root = buildTree(s);
            inOrder(root);
            System.out.println();
        }
    }
    private static TreeNode buildTree(String s) {
        char c = s.charAt(index++);
        if (c == '#') return null;
        TreeNode root = new TreeNode(c);
        root.left = buildTree(s);
        root.right = buildTree(s);
        return root;
    }
    private static void inOrder(TreeNode root) {
        if (root == null) return;
        inOrder(root.left);
        System.out.print(root.value + " ");
        inOrder(root.right);
    }
    private static class TreeNode {
        private final char value;
        private TreeNode left, right;
        private TreeNode(char value) {
            this.value = value;
            this.left = null;
            this.right = null;
        }
    }
}