问题

假设以二叉链表存储的二叉树中，每个结点所含数据元素均为单字母。要求实现二叉树的横向显示问题，如下图所示打印结果。

问题分析

(1) 二叉树的横向显示应是二叉树竖向显示的90°旋转。分析上图可知，这种树形打印格式要求先打印右子树，再打印根，最后打印左子树，按由上而下顺序看，其输出的结点序列为：CFEADB，这恰为逆中序遍历。所以横向显示二叉树的算法为先右子树、再跟结点、再左子树的RDL结构。
(2)在这种输出格式中，结点的左右位置与结点的深度有关，故算法中设置了一个表实当前跟结点层深的参数，以控制输出结点的左、右位置，每当递归进层时层深参数加1。

算法描述

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Tree
{
    class TreeNode<T>
    {
        T data;
        TreeNode<T> LChrild;
        TreeNode<T> RChirld;
        
        public T Data { get => data; set => data = value; }
        internal TreeNode<T> LChrild1 { get => LChrild; set => LChrild = value; }
        internal TreeNode<T> RChirld1 { get => RChirld; set => RChirld = value; }

        public TreeNode(T data)
        {
            this.Data = data;
        }
        public TreeNode()
        {
            this.Data = default(T);
            this.LChrild1 = null;
            this.RChirld1 = null;
        }
    }
}

Program

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Tree
{
    class Program
    {
        static int total = 0; //叶子结点数目

        static void Main(string[] args)
        {
            TreeNode<string> A = new TreeNode<string>("a");
            TreeNode<string> B = new TreeNode<string>("b");
            TreeNode<string> C = new TreeNode<string>("c");
            TreeNode<string> D = new TreeNode<string>("d");
            TreeNode<string> E = new TreeNode<string>("e");
            TreeNode<string> F = new TreeNode<string>("f");
            TreeNode<string> G = new TreeNode<string>("g");
            TreeNode<string> H = new TreeNode<string>("h");

            A.LChrild1 = B;
            B.RChirld1 = D;
            A.RChirld1 = C;
            D.LChrild1 = F;
            D.RChirld1 = G;
            C.RChirld1 = E;
            E.RChirld1 = H;

            PrintTree(A, 0);
        }

        /// <summary>
        /// 逆中序(RDL)遍历实现横向(从屏幕左到屏幕右)梳妆打印
        /// </summary>
        /// <param name="node"></param>
        /// <param name="space"></param>
        static void PrintTree(TreeNode<string> node,int space)
        {
            if (node == null)
                return;
            PrintTree(node.RChirld1, space + 1);
            for (int i = 0; i < space; i++)
            {
                Console.Write("  ");
            }
            Console.WriteLine(node.Data);
            PrintTree(node.LChrild1, space+1);
        }
    }
}