题解 | #二叉树遍历#

import java.util.Scanner;
class TreeNode{
    char val;
    TreeNode left;
    TreeNode right;
    public TreeNode(){

    }
    public TreeNode(char val){
        this.val=val;
    }

}
// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        String tree=in.nextLine();
        TreeNode root=prevOrder(tree);
        inOrder(root);
    }
    public static void inOrder(TreeNode root){
        if(root==null)return;
        inOrder(root.left);
        System.out.print(root.val+" ");
        inOrder(root.right);
    }
    public static int i=0;
    public static TreeNode prevOrder(String s){
        TreeNode root=new TreeNode();
        char ch=s.charAt(i);
        if(ch!='#'){
        root.val=ch;
            i++;
        }else{
            i++;
            return null;
        }  
        root.left=prevOrder(s);
        root.right=prevOrder(s);
        return root;
    }
}