2 xwinterwinterwinterx XwinterwinterwinterX 于 2016.04.11 17:38 提问

请教大家一段代码,跟树的莫里斯循环有关
 #include<stdio.h>
#include<stdlib.h>

/* A binary tree tNode has data, pointer to left child
   and a pointer to right child */
struct tNode
{
   int data;
   struct tNode* left;
   struct tNode* right;
};

/* Function to traverse binary tree without recursion and 
   without stack */
void MorrisTraversal(struct tNode *root)
{
  struct tNode *current,*pre;

  if(root == NULL)
     return; 

  current = root;
  while(current != NULL)
  {                 
    if(current->left == NULL)
    {
      printf(" %d ", current->data);
      current = current->right;      
    }    
    else
    {
      /* Find the inorder predecessor of current */
      pre = current->left;
      while(pre->right != NULL && pre->right != current)
        pre = pre->right;

      /* Make current as right child of its inorder predecessor */
      if(pre->right == NULL)
      {
        pre->right = current;
        current = current->left;
      }

      /* Revert the changes made in if part to restore the original 
        tree i.e., fix the right child of predecssor */   
      else 
      {
        pre->right = NULL;
        printf(" %d ",current->data);
        current = current->right;      
      } /* End of if condition pre->right == NULL */
    } /* End of if condition current->left == NULL*/
  } /* End of while */
}

/* UTILITY FUNCTIONS */
/* Helper function that allocates a new tNode with the
   given data and NULL left and right pointers. */
struct tNode* newtNode(int data)
{
  struct tNode* tNode = (struct tNode*)
                       malloc(sizeof(struct tNode));
  tNode->data = data;
  tNode->left = NULL;
  tNode->right = NULL;

  return(tNode);
}

/* Driver program to test above functions*/
int main()
{

  /* Constructed binary tree is
            1
          /   \
        2      3
      /  \
    4     5
  */
  struct tNode *root = newtNode(1);
  root->left        = newtNode(2);
  root->right       = newtNode(3);
  root->left->left  = newtNode(4);
  root->left->right = newtNode(5); 

  MorrisTraversal(root);

  getchar();
  return 0;
}

请问下面这段代码是什么意思?

   /* Revert the changes made in if part to restore the original 
        tree i.e., fix the right child of predecssor */   
      else 
      {
        pre->right = NULL;
        printf(" %d ",current->data);
        current = current->right;      
      } /* End of if condition pre->right == NULL */

2个回答

XwinterwinterwinterX
XwinterwinterwinterX   2016.04.11 17:39
u011606457
u011606457   2016.06.30 15:45

遍历过程中树结构会改变:
/* Make current as right child of its inorder predecessor */
if(pre->right == NULL)
{
pre->right = current;
current = current->left;
}

        这段带码就是为了还原树结构
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