同上题：

但是这题需要考虑好对当前节点的left和right的next指针如何设置。

 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(TreeLinkNode *root) {
12         if(root == NULL){
13             return;
14         }
15         TreeLinkNode *leftNext = NULL;
16         TreeLinkNode *rightNext = NULL;
17         TreeLinkNode *node = NULL;
18         if(root->left){
19             leftNext = root->right;
20             node = root->next;
21             while(!leftNext && node){
22                 if(node->left){
23                     leftNext = node->left;
24                     break;
25                 }
26                 if(node->right){
27                     leftNext = node->right;
28                     break;
29                 }
30                 node = node->next;
31             }
32             root->left->next = leftNext;
33         }
34         if(root->right){
35             rightNext = NULL;
36             node = root->next;
37             while(!rightNext && node){
38                 if(node->left){
39                     rightNext = node->left;
40                     break;
41                 }
42                 if(node->right){
43                     rightNext = node->right;
44                     break;
45                 }
46                 node = node->next;
47             }
48             root->right->next = rightNext;
49         }
50         connect(root->right);
51         connect(root->left);
52     }
53 };

root->left和root->right顺序不能变。