116. Populating Next Right Pointers in Each Node

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

這個題想法仍是比較單純簡單的，由於是徹底二叉樹，因此先將二叉樹總體最右邊一列的next賦值爲NULL，而後考慮根節點兩棵子樹之間的關係，遞歸。
代碼：

 1 void right_null(TreeLinkNode* root)
 2 {
 3     root->next=NULL;
 4     if (root->right==NULL)
 5         return;
 6     right_null(root->right);
 7 }
 8 
 9 void mid_next(TreeLinkNode* lefts,TreeLinkNode* rights)
10 {
11     lefts->next=rights;
12     TreeLinkNode* le=lefts;
13     TreeLinkNode* ri=rights;
14     while(le->right!=NULL)
15     {
16         le->right->next=ri->left;
17         le=le->right;
18         ri=ri->left;
19     }
20     if (lefts->left==NULL)
21         return;
22     mid_next(lefts->left,lefts->right);
23     mid_next(rights->left,rights->right);
24 }
25 
26 void connect(TreeLinkNode *root)
27 {
28     if(root==NULL)
29         return;
30     right_null(root);
31     if (root->left==NULL)
32         return;
33     mid_next(root->left,root->right);
34 
35 }