剑指Offer：二叉搜索树与双向链表

二叉搜索树与双向链表

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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。

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/*
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)
    {
        if(!pRootOfTree)    return pRootOfTree;
        if(pRootOfTree->left){
            TreeNode *left=toConvert(pRootOfTree->left,nullptr,pRootOfTree);////返回尾节点
            pRootOfTree->left=left;
        }
        if(pRootOfTree->right){
            TreeNode *right=toConvert(pRootOfTree->right,pRootOfTree,nullptr);////返回尾节点
//            pRootOfTree->right=right;
        }
        TreeNode *head;//find head
        while(head->left){
            head=head->left;
        }
        return head;
    }

private:
    TreeNode* toConvert(TreeNode* root,TreeNode *pre,TreeNode *next){
        if(root->left){
            TreeNode *left=toConvert(root->left,pre,root);
            root->left=left;
        }
        else{
            root->left=pre;
            if(pre) pre->right=root;//将右子树的头结点与父节点连接
        }
        if(root->right){
            TreeNode *right=toConvert(root->right,root,next);
//            root->right=right;
            return right;
        }
        else{
            root->right=next;
            return root;
        }
    }

};