題目：給定一顆二叉樹和其中的一個節點，如何找出中序遍歷序列的下一個節點？樹中除了左右指標還有指向雙親的一個指標。

#include<stdio.h>
#include<malloc.h>
#include<assert.h>
typedef struct BinTreeNode{
  struct BinTreeNode *pLeft;
  struct BinTreeNode *pRight;
  struct BinTreeNode *pParent;
  int data;
}BinTreeNode;


BinTreeNode *BuyNode(int data)
{
  BinTreeNode *NewNode = (BinTreeNode *)malloc(sizeof(BinTreeNode));
  assert(NewNode);
  NewNode->data = data;
  NewNode->pLeft = NULL;
  NewNode->pRight = NULL;
  NewNode->pParent = NULL;
  return NewNode;
}


BinTreeNode *FindNextNode(BinTreeNode *pNode)
{
  if(pNode == NULL)
    return NULL;
  BinTreeNode *cur = pNode;
  BinTreeNode *next = pNode->pRight;
  BinTreeNode *parent = pNode->pParent;
  if(next != NULL)
  {
    while(next->pLeft != NULL)  //情況1
      next = next->pLeft;
  }
  else if(parent != NULL)
  {
    if(parent != NULL && cur == parent->pRight)//情況2和3
    {
       cur = parent;
       parent = parent->pParent;
    }
    next = parent;
  }
  return next;
}

void test()
{
  BinTreeNode *Node1 = BuyNode(1);
  BinTreeNode *Node2 = BuyNode(2);
  BinTreeNode *Node3 = BuyNode(3);
  BinTreeNode *Node4 = BuyNode(4);
  BinTreeNode *Node5 = BuyNode(5);
  BinTreeNode *Node6 = BuyNode(6);
  BinTreeNode *Node7 = BuyNode(7);
  BinTreeNode *Node8 = BuyNode(8);
  BinTreeNode *Node9 = BuyNode(9);


  Node1->pLeft = Node2;
  Node1->pRight = Node3;

  Node2->pLeft = Node4;
  Node2->pRight = Node5;

  Node3->pLeft = Node6;
  Node3->pRight = Node7;
  
  Node5->pLeft = Node8;
  Node5->pRight = Node9;

  Node8->pParent = Node5;
  Node9->pParent = Node5;

  Node5->pParent = Node2;
  Node2->pParent = Node1;

  Node4->pParent = Node2;

  Node6->pParent = Node3;
  Node7->pParent = Node3;

  Node3->pParent = Node1;

  BinTreeNode *NextRet = FindNextNode(Node8);
  printf("Node8的下一個節點是%d\n",NextRet->data);
}

int main()
{
  test();
  return 0;
}