二叉树的Morris遍历

　　二叉树的遍历，除了上篇文章中的传统递归和使用的栈结构的非递归方式，还有如下这种Morris遍历方式，该算法的构思非常巧妙：利用前驱空闲的rightChild指针指向当前节点，形成一个环。时间复杂度和前面两种一样，还是O(n)，但是空间复杂度由O(n)直接下降到了O(1)。代码如下：

 /*************************************************************************
     > File Name: MorrisTraversal.c
     > Description: 线索二叉树的实现
     > Author: Yves
     > E-mail:
     > Created Time: 2015-5-23. 22:51:16
  ************************************************************************/

 #include <stdio.h>
 #include <stdlib.h>

 typedef char ElemType;
 typedef struct tagBiTreeNode
 {
     ElemType data;
     struct tagBiTreeNode* leftChild;
     struct tagBiTreeNode* rightChild;
 }BiTreeNode, *pBiTreeNode;//指向BiTNode的指针

 static void CreatBiTree(pBiTreeNode *root);//创建二叉树
 static void PreOrderMorrisTraversal(pBiTreeNode root);//前序Morris遍历
 static void InOrderMorrisTraversal(pBiTreeNode root);//中序Morris遍历
 static void PostOrderMorrisTraversal(pBiTreeNode root);//后序Morris遍历

 pBiTNode pre;

 int main(void)
 {
     pBiTreeNode root;
     printf("Please input the node of the tree(preorder sequence): ");
     CreatBiTree(&root);
     printf("Traverse the tree in PreOrderMorrisTraversal\n");
     PreOrderMorrisTraversal(root);
     printf("Traverse the tree in InOrderMorrisTraversal\n");
     InOrderMorrisTraversal(root);
     printf("Traverse the tree in PostOrderMorrisTraversal\n");
     PostOrderMorrisTraversal(root)

     return ;
 }

 static void CreatBiTree(pBiTreeNode *root)
 {
     ElemType c;
     scanf("%c",&c);
     if(c == '#')
     {
         *root = NULL;
     }else
     {
         *root = (pBiTreeNode)malloc(sizeof(BiTreeNode));
         (*root)->data = c;
         CreatBiTree(&(*root)->leftChild);
         CreatBiTree(&(*root)->rightChild);
     }
 }

 static void PreOrderMorrisTraversal(pBiTreeNode root)
 {
     if(root == NULL)
     {
         return;
     }
     pBiTreeNode cur,pre,temp;
     cur = root;
     while(cur != NULL)
     {
         if(!cur->leftChild)
         {
             printf("%c ", cur->data);
             pre = cur;
             cur = cur->rightChild;
         }else
         {
             for(temp = cur->leftChild; temp->rightChild != NULL && temp->rightChild != cur; temp = temp->rightChild);
             if(temp->rightChild == NULL)
             {
                 temp->rightChild = cur;
                 printf("%c ", cur->data);
                 pre = cur;
                 cur = cur->leftChild;
             }else
             {

                 temp->rightChild = NULL;
                 cur = cur->rightChild;
             }
         }
     }
 }

 static void InOrderMorrisTraversal(pBiTreeNode root)
 {
     if(root == NULL)
     {
         return;
     }
     pBiTreeNode cur,pre,temp;
     cur = root;
     while(cur != NULL)
     {
         if(!cur->leftChild)
         {
             printf("%c ", cur->data);
             pre = cur;
             cur = cur->rightChild;
         }else
         {
             for(temp = cur->leftChild; temp->rightChild != NULL && temp->rightChild != cur; temp = temp->rightChild);
             if(temp->rightChild == NULL)
             {
                 temp->rightChild = cur;
                 cur = cur->leftChild;
             }else /*Meaning the left tree has been accessed completely.*/
             {
                 printf("%c ", cur->data);
                 temp->rightChild = NULL;
                 pre = cur;
                 cur = cur->rightChild;
             }
         }
     }
 }

 static void PostOrderMorrisTraversal(pBiTreeNode root)
 {
     //coding
 }