二叉树定义（递归方式）：

class Node    {        public int Key;        public Node Left, Right;        public Node(int item)        {            Key = item;            Left = Right = null;        }    }    class BinaryTree    {        // Root of Binary Tree        public Node Root;        public BinaryTree()        {            Root = null;        }        /* Given a binary tree, print its nodes according to the "bottom-up" postorder traversal. */        public void printPostorder(Node node)        {            if (node == null)                return;            // first recur on left subtree            printPostorder(node.Left);            // then recur on right subtree            printPostorder(node.Right);            // now deal with the node            Console.WriteLine(node.Key + " ");        }        /* Given a binary tree, print its nodes in inorder*/        public void printInorder(Node node)        {            if (node == null)                return;            /* first recur on left child */            printInorder(node.Left);            /* then print the data of node */            Console.WriteLine(node.Key + " ");            /* now recur on right child */            printInorder(node.Right);        }        /* Given a binary tree, print its nodes in preorder*/        public void printPreorder(Node node)        {            if (node == null)                return;            /* first print data of node */            Console.WriteLine(node.Key + " ");            /* then recur on left sutree */            printPreorder(node.Left);            /* now recur on right subtree */            printPreorder(node.Right);        }        // Wrappers over above recursive functions        public void printPostorder() { printPostorder(Root); }        public void printInorder() { printInorder(Root); }        public void printPreorder() { printPreorder(Root); }    }

前、中、后序的遍历：

/**         * 二叉树         */        static void Main(string[] args)        {            /**             *             1             *            / \             *          2    3             *         / \             *        4   5             * **/            BinaryTree tree = new BinaryTree();            tree.Root = new Node(1);            tree.Root.Left = new Node(2);            tree.Root.Right = new Node(3);            tree.Root.Left.Left = new Node(4);            tree.Root.Left.Right = new Node(5);            Console.WriteLine("Preorder traversal of binary tree is ");            tree.printPreorder();            Console.WriteLine("\nInorder traversal of binary tree is ");            tree.printInorder();            Console.WriteLine("\nPostorder traversal of binary tree is ");            tree.printPostorder();            Console.ReadKey();        }

输出结果：

还有使用非递归的方式实现遍历的方式，以及删除节点等处理请参考：https://blog.csdn.net/sinat_36246371/article/details/53351204

后序再研究，目前记不清。。。。