Connect Level Order Siblings (medium)

import java.util.*;
class TreeNode {
  int val;
  TreeNode left;
  TreeNode right;
  TreeNode next;
  TreeNode(int x) {
    val = x;
    left = right = next = null;
  }
  // level order traversal using 'next' pointer
  void printLevelOrder() {
    TreeNode nextLevelRoot = this;
    while (nextLevelRoot != null) {
      TreeNode current = nextLevelRoot;
      nextLevelRoot = null;
      while (current != null) {
        System.out.print(current.val + " ");
        if (nextLevelRoot == null) {
          if (current.left != null)
            nextLevelRoot = current.left;
          else if (current.right != null)
            nextLevelRoot = current.right;
        }
        current = current.next;
      }
      System.out.println();
    }
  }
};
class ConnectLevelOrderSiblings {
  public static void connect(TreeNode root) {
    // TODO: Write your code here
  }
  public static void main(String[] args) {
    TreeNode root = new TreeNode(12);
    root.left = new TreeNode(7);
    root.right = new TreeNode(1);
    root.left.left = new TreeNode(9);
    root.right.left = new TreeNode(10);
    root.right.right = new TreeNode(5);
    ConnectLevelOrderSiblings.connect(root);
    System.out.println("Level order traversal using 'next' pointer: ");
    root.printLevelOrder();
  }
}