二叉搜索树与双向链表

题目描述
输入一棵二叉搜索树，将该二叉搜索树转换成一个排序的双向链表。要求不能创建任何新的结点，只能调整树中结点指针的指向。

/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public TreeNode Convert(TreeNode pRootOfTree) {
        TreeNode lastNode =null;
		TreeNode headNode=ConvertNode(pRootOfTree, lastNode);
		while (headNode != null && headNode.left != null) {
		headNode = headNode.left;
		}
		return headNode;
    }
    public static TreeNode ConvertNode(TreeNode rootTree, TreeNode lastNode) {
		if (rootTree == null) {
			return null;
		}
		if (rootTree.left != null) {
			lastNode=ConvertNode(rootTree.left, lastNode);
		}
		rootTree.left = lastNode;
		if (lastNode != null) {
			lastNode.right = rootTree;
		}
		lastNode = rootTree;
		if (rootTree.right != null) {
			lastNode=ConvertNode(rootTree.right, lastNode);
		}
		return lastNode;
	}
}