【树】

 1 /*
 2 // Definition for a Node.
 3 class Node {
 4 public:
 5     int val;
 6     Node* left;
 7     Node* right;
 8     Node* next;
 9 
10     Node() : val(0), left(NULL), right(NULL), next(NULL) {}
11 
12     Node(int _val) : val(_val), left(NULL), right(NULL), next(NULL) {}
13 
14     Node(int _val, Node* _left, Node* _right, Node* _next)
15         : val(_val), left(_left), right(_right), next(_next) {}
16 };
17 */
18 
19 class Solution {
20 public:
21     Node* connect(Node *root)
22     {
23         if(root == NULL)
24         {
25             return root;
26         }
27 
28         Node *leftwall = root;
29         while(leftwall != NULL)
30         {
31             Node *across = leftwall;
32             while(across != NULL)
33             {
34                 //如果左子树不为空，则设置其左子树的next域
35                 if(across->left != NULL)
36                 {
37                     across->left->next = across->right;
38                 }
39 
40                 //如果右子树不为空，且该右子树的叔叔结点的左孩子不为空
41                 if(across->right != NULL && across->next != NULL)
42                 {
43                     across->right->next = across->next->left;
44                 }
45                 across = across->next;
46             }
47 
48             leftwall = leftwall->left;
49         }
50 
51         return root;
52     }
53 };