题解 | #二叉搜索树与双向链表#

看了评论区大佬方法，pre要加引用或者干脆设置为一个成员变量，因为回溯后还要用到pre

class Solution {
public:
    void backtra(TreeNode* cur,TreeNode*& pre){
        if(!cur) return;
        backtra(cur->left, pre);
        cur->left=pre;
        if(pre) pre->right=cur;
        pre=cur;
        backtra(cur->right,pre);
    }
    TreeNode* Convert(TreeNode* pRootOfTree) {
        if(!pRootOfTree) return pRootOfTree;
        TreeNode* pre =NULL;
        backtra(pRootOfTree, pre);
        TreeNode* ans =pRootOfTree;
        while(ans->left){
            ans=ans->left;
        }
        return ans;
    }
};