LeetCode Populating Next Right Pointers in Each Node

 // 4ms  120ms
 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         // Start typing your C/C++ solution below
13         // DO NOT write int main() function
14         TreeLinkNode *p=root,*q;
15         if(p==NULL)
16             return ;
17         if(p->left==NULL)
18             return ;
19         root->left->next=root->right;
20         
21         q=root->left;
22         
23         while(q->left)
24         {
25             p=q;
26             while(p->next)
27             {
28                 p->left->next=p->right;
29                 p->right->next=p->next->left;
30                 p=p->next;
31             }
32             p->left->next=p->right;
33             q=q->left;
34         }
35     }
36 };