二叉树的递归遍历和非递归遍历（附详细例子）

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转：http://blog.csdn.net/sheepmu/article/details/28941285

二叉树的递归遍历和非递归遍历（附详细例子）

二叉树的遍历主要有递归实现和非递归实现，递归实现比较好理解，非递归实现主要是利用了栈的思想，后进先出，本文实现二叉树的非递归遍历主要是用了LinkedList可以当做栈使用的功能。具体例子如下：

import java.util.LinkedList; public class BinaryTree{    private TreeNode root;// 根节点    public BinaryTree()    {    }    public BinaryTree(TreeNode root)    {        this.root = root;    }    public TreeNode getRoot()    {        return root;    }    public void setRoot(TreeNode root)    {        this.root = root;    }    /**     * 节点类     */    private static class TreeNode    {        private String data = null;// 数据部分        private TreeNode left;// 左节点的引用        private TreeNode right;// 右节点的引用        public TreeNode(String data, TreeNode left, TreeNode right)//节点的构造函数，测试函数中创建节点就是用了它        {            this.data = data;            this.left = left;            this.right = right;        }             public String getData()//节点类的get和set方法        {            return data;        }        public void setData(String data)        {            this.data = data;        }        public TreeNode getLeft()        {            return left;        }        public void setLeft(TreeNode left)        {            this.left = left;        }        public TreeNode getRight()        {            return right;        }        public void setRight(TreeNode right)        {            this.right = right;        }    }     /**     *  递归 前续遍历     */    public void preOrder(TreeNode node)    {        if (node != null)        {            System.out.print(node.getData()+"  ");            preOrder(node.getLeft());            preOrder(node.getRight());        }    }    /**     *  递归 中续遍历     */    public void inOrder(TreeNode node)    {        if (node != null)        {        inOrder(node.getLeft());        System.out.print(node.getData()+"  ");        inOrder(node.getRight());        }    }    /**     *  递归 后续遍历     */    public void postOrder(TreeNode node)    {        if (node != null)        {        postOrder(node.getLeft());        postOrder(node.getRight());         System.out.print(node.getData()+"  ");        }    }        /**     *  非递归 前续遍历     */    public void preOrderNoRecursion()     {         LinkedList<TreeNode> stack = new LinkedList<TreeNode>();         stack.push(root);         TreeNode current = null;         while (!stack.isEmpty())         {             current = stack.pop();             System.out.print(current.data+"  ");             if (current.getRight() != null)                 stack.push(current.getRight());             if (current.getLeft() != null)                 stack.push(current.getLeft());         }         System.out.println();     }         /**     *  非递归 中续遍历     */    public void inorderNoRecursion()     {         LinkedList<TreeNode> stack = new LinkedList<TreeNode>();         TreeNode current = root;         while (current != null || !stack.isEmpty())         {             while(current != null)             {                 stack.push(current);                 current = current.getLeft();             }             if (!stack.isEmpty())             {                 current = stack.pop();                 System.out.print(current.data+"  ");                 current = current.getRight();             }         }         System.out.println();     }         /**     *  非递归 后续遍历     */    public void postorderNoRecursion()     {         TreeNode rNode = null;         TreeNode current = root;         LinkedList<TreeNode> stack = new LinkedList<TreeNode>();         while(current != null || !stack.isEmpty())         {             while(current != null)             {                 stack.push(current);                 current = current.getLeft();             }             current = stack.pop();             while (current != null && (current.getRight() == null ||current.getRight() == rNode))             {                 System.out.print(current.data+"  ");                 rNode = current;                 if (stack.isEmpty())                {                     System.out.println();                     return;                 }                 current = stack.pop();             }             stack.push(current);             current = current.getRight();         }              }         public static void main(String[] args)    {        TreeNode l2 = new TreeNode("E", null, null);//这五行构造一棵二叉树        TreeNode r2 = new TreeNode("D", null, null);        TreeNode l1 = new TreeNode("B",null, r2);// 根节点左子树        TreeNode r1 = new TreeNode("C", l2, null);// 根节点右子树        TreeNode root = new TreeNode("A", l1, r1);// 创建根节点        BinaryTree bt = new BinaryTree(root);        System.out.print(" 递归 前序遍历------->");        bt.preOrder(bt.getRoot());        System.out.print(" 非递归 前序遍历------->");        bt.preorderNoRecursion();        System.out.print(" 递归 中序遍历------->");        bt.inOrder(bt.getRoot());        System.out.print(" 非递归 中序遍历------->");        bt.inorderNoRecursion();        System.out.print(" 递归 后序遍历------->");        bt.postOrder(bt.getRoot());        System.out.print(" 非递归 后序遍历------->");        bt.postorderNoRecursion();            }}

递归前序遍历------->A B D C E 非递归前序遍历------->A B D C E
递归中序遍历------->B D A E C 非递归中序遍历------->B D A E C
递归后序遍历------->D B E C A 非递归后序遍历------->D B E C A

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