LeetCode 117 Populating Next Right Pointers in Each Node II

/**
 * 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);
    }
}