Populating Next Right Pointers in Each Node

lc_116.cpp

/**
 * 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) {
        //assigning the pointer level by level, and queue is not needed because the next pointer works the same as queue
        if(root == NULL)
            return;
        root->next = NULL;
        TreeLinkNode *seed = root;
        while(seed->left != NULL)
        {
            TreeLinkNode *line = seed;
            //assign children's next pointer
            while(line->next)
            {
                line->left->next = line->right;
                line->right->next = line->next->left;
                line = line->next;
            }
            //tail
            line->left->next = line->right;
            line->next = NULL;
            line->right->next = NULL;
            
            //iterate to the next
            seed = seed->left;
        }
    }
};