面试题27 二叉搜索树与双向链表

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。

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    void convertNode(TreeNode *pNode, TreeNode **pLast){
        if (pNode == NULL){
            return;
        }
        TreeNode *pCur = pNode;
        if (pCur->left != NULL){
            convertNode(pNode->left, pLast);
        }
        pCur->left = *pLast;
        if (*pLast != NULL){
            (*pLast)->right = pCur;
        }
        *pLast = pCur;
        if (pCur->right != NULL){
            convertNode(pCur->right, pLast);
        }
    }
    
    TreeNode* Convert(TreeNode* pRootOfTree)
    {
        TreeNode *pLast = NULL;
        convertNode(pRootOfTree, &pLast);
        TreeNode *pHead = pLast;
        
        while (pHead != NULL && pHead->left != NULL){
            pHead = pHead->left;
        }
        return pHead;
    }
};