剑指offer——面试题27：二叉搜索树与双向链表

BinaryTreeNode* Convert(BinaryTreeNode* pRootOfTree)
{
BinaryTreeNode *pLastNodeInList = NULL;
ConvertNode(pRootOfTree, &pLastNodeInList);

// pLastNodeInList指向双向链表的尾结点，
// 我们需要返回头结点
BinaryTreeNode *pHeadOfList = pLastNodeInList;
while(pHeadOfList != NULL && pHeadOfList->m_pLeft != NULL)
pHeadOfList = pHeadOfList->m_pLeft;

return pHeadOfList;
}

void ConvertNode(BinaryTreeNode* pNode, BinaryTreeNode** pLastNodeInList)
{
if(pNode == NULL)
return;

BinaryTreeNode *pCurrent = pNode;

if (pCurrent->m_pLeft != NULL)
ConvertNode(pCurrent->m_pLeft, pLastNodeInList);

pCurrent->m_pLeft = *pLastNodeInList;
if(*pLastNodeInList != NULL)
(*pLastNodeInList)->m_pRight = pCurrent;

*pLastNodeInList = pCurrent;

if (pCurrent->m_pRight != NULL)
ConvertNode(pCurrent->m_pRight, pLastNodeInList);
}