Leetcode Populating Next Right Pointers in Each Node II

/**
* 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) {
// IMPORTANT: Please reset any member data you declared, as
// the same Solution instance will be reused for each test case.
TreeLinkNode *first, *prev, *head = root;
while(head){
first = NULL, prev = NULL;
while(head){
if(!first)  first = head->left ? head->left : head->right;
if(head->left){
if(prev)    prev->next = head->left;
prev = head->left;
}
if(head->right){
if(prev)    prev->next = head->right;
prev = head->right;
}
head = head->next;
}
head = first;
}
}
};