hello-algo/codes/csharp/chapter_tree/binary_tree_dfs.cs

/**
 * File: binary_tree_dfs.cs
 * Created Time: 2022-12-23
 * Author: haptear (haptear@hotmail.com)
 */

namespace hello_algo.chapter_tree;

public class binary_tree_dfs {
    readonly List<int> list = new();

    /* 前序遍历 */
    void PreOrder(TreeNode? root) {
        if (root == null) return;
        // 访问优先级：根节点 -> 左子树 -> 右子树
        list.Add(root.val);
        PreOrder(root.left);
        PreOrder(root.right);
    }

    /* 中序遍历 */
    void InOrder(TreeNode? root) {
        if (root == null) return;
        // 访问优先级：左子树 -> 根节点 -> 右子树
        InOrder(root.left);
        list.Add(root.val);
        InOrder(root.right);
    }

    /* 后序遍历 */
    void PostOrder(TreeNode? root) {
        if (root == null) return;
        // 访问优先级：左子树 -> 右子树 -> 根节点
        PostOrder(root.left);
        PostOrder(root.right);
        list.Add(root.val);
    }

    [Test]
    public void Test() {
        /* 初始化二叉树 */
        // 这里借助了一个从数组直接生成二叉树的函数
        TreeNode? root = TreeNode.ListToTree(new List<int?> { 1, 2, 3, 4, 5, 6, 7 });
        Console.WriteLine("\n初始化二叉树\n");
        PrintUtil.PrintTree(root);

        list.Clear();
        PreOrder(root);
        Console.WriteLine("\n前序遍历的节点打印序列 = " + string.Join(",", list));

        list.Clear();
        InOrder(root);
        Console.WriteLine("\n中序遍历的节点打印序列 = " + string.Join(",", list));

        list.Clear();
        PostOrder(root);
        Console.WriteLine("\n后序遍历的节点打印序列 = " + string.Join(",", list));
    }
}