/** * 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 mostLeft = root;                while (mostLeft != null) {            root = mostLeft;            while(root != null) {                if (root.left != null && root.right != null) {                    root.left.next = root.right;                    root.right.next = getNextNode(root.next);                } else if (root.left != null || root.right != null) {                    getNextNode(root).next = getNextNode(root.next);                }                root = root.next;            }            mostLeft = getNextNode(mostLeft);        }    }        private TreeLinkNode getNextNode(TreeLinkNode root) {        if (root == null) {            return null;        }        if (root.left != null) {            return root.left;        }                if (root.right != null) {            return root.right;        }                return getNextNode(root.next);    }}