Populating Next Right Pointers in Each Node

/** * Definition for binary tree with next pointer. * public class TreeLinkNode { *     int val; *     TreeLinkNode left, right, next; *     TreeLinkNode(int x) { val = x; } * } */public class Solution {    public void connect(TreeLinkNode root) {        if (root == null) return;        TreeLinkNode levelStart = root;        TreeLinkNode levelRun = null;        while(levelStart.left != null){            levelRun = levelStart;            while(levelRun != null){                levelRun.left.next = levelRun.right;                if (levelRun.next != null){                    levelRun.right.next = levelRun.next.left;                }                levelRun = levelRun.next;            }            levelStart = levelStart.left;        }    }}