转载 把二元查找树转变成排序的双向链表

http://zhedahht.blog.163.com/blog/static/254111742007127104759245/

题目：输入一棵二元查找树，将该二元查找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，只调整指针的指向。

　　比如将二元查找树
10
/ /
6 14
/ / /　 /
　4 8 12 　 16

转换成双向链表
4=6=8=10=12=14=16。
很多与树相关的题目都是用递归的思路来解决，本题也不例外。

当我们到达某一结点准备调整以该结点为根结点的子树时，先调整其左子树将左子树转换成一个排好序的左子链表，再调整其右子树转换右子链表。最近链接左子链表的最右结点（左子树的最大结点）、当前结点和右子链表的最左结点（右子树的最小结点）。从树的根结点开始递归调整所有结点。

struct BSTreeNode // a node in the binary search tree
{
int          m_nValue; // value of node
BSTreeNode  *m_pLeft;  // left child of node
BSTreeNode  *m_pRight; // right child of node
};

///////////////////////////////////////////////////////////////////////
// Covert a sub binary-search-tree into a sorted double-linked list
// Input: pNode - the head of the sub tree
//        asRight - whether pNode is the right child of its parent
// Output: if asRight is true, return the least node in the sub-tree
//         else return the greatest node in the sub-tree
///////////////////////////////////////////////////////////////////////
BSTreeNode* ConvertNode(BSTreeNode* pNode, bool asRight)
{
if(!pNode)
return NULL;

BSTreeNode *pLeft = NULL;
BSTreeNode *pRight = NULL;

// Convert the left sub-tree
if(pNode->m_pLeft)
pLeft = ConvertNode(pNode->m_pLeft, false);

// Connect the greatest node in the left sub-tree to the current node
if(pLeft)
{
pLeft->m_pRight = pNode;
pNode->m_pLeft = pLeft;
}

// Convert the right sub-tree
if(pNode->m_pRight)
pRight = ConvertNode(pNode->m_pRight, true);

// Connect the least node in the right sub-tree to the current node
if(pRight)
{
pNode->m_pRight = pRight;
pRight->m_pLeft = pNode;
}

BSTreeNode *pTemp = pNode;

// If the current node is the right child of its parent,
// return the least node in the tree whose root is the current node
if(asRight)
{
while(pTemp->m_pLeft)
pTemp = pTemp->m_pLeft;
}
// If the current node is the left child of its parent,
// return the greatest node in the tree whose root is the current node
else
{
while(pTemp->m_pRight)
pTemp = pTemp->m_pRight;
}

return pTemp;
}

///////////////////////////////////////////////////////////////////////
// Covert a binary search tree into a sorted double-linked list
// Input: the head of tree
// Output: the head of sorted double-linked list
///////////////////////////////////////////////////////////////////////
BSTreeNode* Convert(BSTreeNode* pHeadOfTree)
{
// As we want to return the head of the sorted double-linked list,
// we set the second parameter to be true
return ConvertNode(pHeadOfTree, true);
}