Populating Next Right Pointers in Each Node

Description:

Given a binary tree

    struct TreeLinkNode {

      TreeLinkNode *left;

      TreeLinkNode *right;

      TreeLinkNode *next;

    }

Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL.

Initially, all next pointers are set to NULL.

Note:

• You may only use constant extra space.
• You may assume that it is a perfect binary tree (ie, all leaves are at the same level, and every parent has two children).

For example,
Given the following perfect binary tree,

         1

       /  \

      2    3

     / \  / \

    4  5  6  7

 

After calling your function, the tree should look like:

         1 -> NULL

       /  \

      2 -> 3 -> NULL

     / \  / \

    4->5->6->7 -> NULL

Code:

 1  void connect(TreeLinkNode *root) {

 2         if (NULL == root)

 3             return ;

 4         while (root->left != NULL)

 5         {

 6             TreeLinkNode * p = root;

 7             while (p)

 8             {

 9                 p->left->next = p->right;

10                 if (p->next)

11                     p->right->next = p->next->left;

12                 p = p->next;

13             }

14            root = root->left;

15         }

16     }

PS:注意与另一题目Populating Next Right Pointers in Each NodeII的区别，本题要求使用常量空间求解。可以借助next指针实现各兄弟结点之间的连接。