剑指Offer（二十六）-- 二叉搜索树和双向链表

class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

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

    }

}

public class Solution {
    // 头节点
    public TreeNode head = null;
    // 尾节点
    public TreeNode end = null;

    public TreeNode Convert(TreeNode pRootOfTree) {
        invert(pRootOfTree);
        return head;
    }

    public void invert(TreeNode node) {
        if (node == null) {
            return;
        }
        invert(node.left);
        if (end == null) {
            head = node;
            end =node;
        }else{
            end.right = node;
            node.left = end;
            end =node;
        }
        invert(node.right);
    }
}