用c#写个二叉树前序遍历

以下是使用C#编写的二叉树前序遍历的示例代码：

using System;

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

    public TreeNode(int val = 0, TreeNode left = null, TreeNode right = null)
    {
        this.val = val;
        this.left = left;
        this.right = ;
    }
}

public class BinaryTree
{
    public void PreorderTraversal(TreeNode root)
    {
        if (root == null)
            return;

        Console.Write(root.val + " ");
        PreorderTraversal(root.left);
        PreorderTraversal(root.right);
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        // 创建二叉树
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(3);
        root.left.left = new TreeNode(4);
        root.left.right = new TreeNode(5);

        // 前序遍历二叉树
        BinaryTree bt = new BinaryTree();
        Console.WriteLine("前序遍历结果：");
        bt.PreorderTraversal(root);
    }
}