LeetCode(116) Populating Next Right Pointers in Each Node

[code]/**
 * 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) {
        if(root == NULL)

            return;

        if(root->left == NULL)

            return;

        if(root->next == NULL) {

            root->left->next = root->right;
            root->right->next = NULL;

        }

        if(root->next != NULL) {

            root->left->next = root->right;
            root->right->next = root->next->left;

        }

        connect(root->left);

        connect(root->right);

    }
};