LeetCode --- Populating Next Right Pointers in Each Node II

题目链接

Problem description:

Follow up for problem "Populating Next Right Pointers in Each Node".

What if the given tree could be any binary tree? Would your previous solution still work?

Note:

• You may only use constant extra space.

For example,
Given the following binary tree,

         1

       /  \

      2    3

     / \    \

    4   5    7

After calling your function, the tree should look like:

         1 -> NULL

       /  \

      2 -> 3 -> NULL

     / \    \

    4-> 5 -> 7 -> NULL

Accepted Code:

 1 /**  2  * Definition for binary tree with next pointer.  3  * struct TreeLinkNode {  4  * int val;  5  * TreeLinkNode *left, *right, *next;  6  * TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {}  7  * };  8  */

 9 class Solution { 10 public: 11     void connect_helper(TreeLinkNode *root) { 12         if (root == NULL) return ; 13         // when root is a leaf node

14         if (root->left == NULL && root->right == NULL) return; 15         if (root->left != NULL && root->right != NULL) 16             root->left->next = root->right; 17         

18         TreeLinkNode *p = NULL, *head = root; 19         // iterator on the level

20         while (head->next != NULL && head->next->left == NULL && head->next->right == NULL) 21             head = head->next; 22         

23         if (head->next != NULL) { 24             if (head->next->left != NULL) 25                 p = head->next->left; 26             else

27                 p = head->next->right; 28  } 29         // right child is not null

30         if (root->right != NULL) 31             root->right->next = p; 32         else 

33             root->left->next = p; 34         // recursive solve right and left child of root 35         // attention that the right child should be proceeded first

36         connect_helper(root->right); 37         connect_helper(root->left); 38  } 39     void connect(TreeLinkNode *root) { 40         // root = NULL

41         if (root == NULL) return ; 42         // deal root node

43         root->next = NULL; 44          

45  connect_helper(root); 46  } 47 };