題目描述★★★★：
輸入一棵二叉搜索樹，將該二叉搜索樹轉(zhuǎn)換成一個排序的雙向鏈表。要求不能創(chuàng)建任何新的結(jié)點(diǎn)，只能調(diào)整樹中結(jié)點(diǎn)指針的指向。

難點(diǎn)坑點(diǎn)
太難了不想說

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    TreeNode* Convert(TreeNode* pRootOfTree)
    {
        TreeNode* pre=nullptr ;
        TreeNode* first=nullptr;
        if(pRootOfTree==nullptr)
            return first;
        linetree(pRootOfTree,pre);
        while(pre->left!=nullptr)
            pre=pre->left;
        return pre;
    }
    void linetree(TreeNode* current, TreeNode* &pre)
    {
        if(current==nullptr)
            return ;
        linetree(current->left,pre);
        current->left=pre;
        if(pre)
            pre->right=current;
        pre=current;
        linetree(current->right,pre);
    }
};