[Leetcode] Populating Next Right Pointers in Each Node

/**
 * Definition for binary tree with next pointer.
 * struct TreeLinkNode {
 *  int val;
 *  TreeLinkNode *left, *right, *next;
 *  TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {}
 * };
 */
class Solution {
public:
    void connect(TreeLinkNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (!root) return;
        
        if (!root->left || !root->right)
            return;
            
        TreeLinkNode* next = NULL;
        TreeLinkNode* p = root;
        
        while (p)
        {
            if (p->next)
                next = p->next->left;
            else
                next = NULL;
            
            p->left->next = p->right;
            p->right->next = next;
            p = p->next;
        }
        connect(root->left);
    }
};