package com.gylhaut.bean;public class TreeNode
     
       {    public T data;    public TreeNode left;    public TreeNode right;    public TreeNode(T data) {        this.left = null;        this.right = null;        this.data = data;    }}
     

　算法实现：

package com.gylhaut.util;import com.gylhaut.bean.TreeNode;public class BinaryTreeHelper {    /**     * 指向头节点     * @param root     * @return     */    public static TreeNode convert(TreeNode root){        root=convert2Link(root);        while (root.left != null){            root = root.left;        }        return root;    }    /**     * 搜索二叉树转成双向链表     * @param root     * @return     */    public static TreeNode convert2Link(TreeNode root){        if(root == null|| (root.left == null && root.right == null)){            return root;        }        TreeNode tmp = null;        if(root.left != null){           tmp= convert2Link(root.left);           while (tmp.right != null){               tmp = tmp.right;           }           tmp.right = root;           root.left = tmp;        }        if (root.right !=null){            tmp = convert2Link(root.right);            while (tmp.left != null){                tmp = tmp.left;            }            tmp.left = root;            root.right = tmp;        }        return root;    }}