何海涛100题（1）自己心得

原题在这里：

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

自己的总结：

为了将一个二叉查找树转变为双向链表，在递归将左子树右子树都变成双向链表后，需要将左子树中的最大元素和当前元素串联起来（右子树中的最小元素同理），对于这一操作，我们不可以先进入子树中再操作，因为从当前节点访问子节点（both左右）都很容易（有指针，直接访问就好），但是从子节点访问父亲节点没法直接访问（无指针，无法直接访问）。

#include <iostream>
using namespace std;


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
    };

BSTreeNode* ConvertNode(BSTreeNode* pNode, bool asRight);

int main()
{
    BSTreeNode node1, node2, node3;
    node1.m_nValue = 2;
    node2.m_nValue = 1;
    node3.m_nValue = 3;
    node1.m_pLeft = &node2;
    node1.m_pRight = &node3;
    node2.m_pLeft = 0;
    node2.m_pRight = 0;
    node3.m_pLeft = 0;
    node3.m_pRight = 0;
    ConvertNode(&node1, 0);
    cout<<"node 2 = "<<node2.m_nValue<<endl;
    cout<<"node 2's next = "<<node2.m_pRight->m_nValue<<endl;
    cout<<"node 2's next's next = "<<node2.m_pRight->m_pRight->m_nValue;
    return 1;
}

///////////////////////////////////////////////////////////////////////
// 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;//左子树中的最大元素的右指针指向当前元素
            pNode->m_pLeft = pLeft;//当前元素的左指针指向左子树中的最大元素
      }

      // 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;//同左子树中的连接操作
            pRight->m_pLeft = pNode;//见上
      }

      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;
}