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。

解法

中序排序

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    void GetConvertTail(TreeNode* pRootOfTree,TreeNode** pLastNode)
    {
        if(pRootOfTree == NULL)
        {
            return;
        }
        
        TreeNode* curNode = pRootOfTree;
        if(curNode->left)
        {
            GetConvertTail(curNode->left,pLastNode);
        }
        curNode->left = *pLastNode;
        if(*pLastNode)
        {
            (*pLastNode)->right = curNode;
        }
        *pLastNode = curNode;
        
        if(curNode->right)
        {
            GetConvertTail(curNode->right,pLastNode);
        }
        
    }
    
    TreeNode* Convert(TreeNode* pRootOfTree)
    {
        if(pRootOfTree == NULL)
        {
            return NULL;
        }
        
        TreeNode* result = NULL;
        GetConvertTail(pRootOfTree,&result);
        while(result && result->left)
        {
            result = result->left;
        }
        
        return result;
    }
};