题解 | #二叉树遍历#

import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;

public class Main {
    static class TreeNode{
        char val;
        TreeNode left;
        TreeNode right;
        public TreeNode(char val){
            this.val = val;
        }
    }

    public static TreeNode buildTree(Queue<Character> input){
        if (input == null){
            return null;
        }
        char nodeVal = input.remove();
        if (nodeVal == '#'){
            return null;
        }

        TreeNode node = new TreeNode(nodeVal);

        node.left = buildTree(input);
        node.right = buildTree(input);

        return node;
    }

    public static void look(TreeNode root){
        if (root == null){
            return;
        }

        look(root.left);
        System.out.printf("%c ", root.val);;
        look(root.right);
    }

    public static void main(String[] args) {
        Scanner sca = new Scanner(System.in);
       while (sca.hasNextLine()){
           String str = null;
           Queue<Character> input = new LinkedList<>();
           if (sca.hasNext()){
               str = sca.nextLine();
           }
           if (str != null){
               for (char ch : str.toCharArray()){
                   input.add(ch);
               }
               TreeNode root = buildTree(input);
               look(root);
           }
       }
    }
}